MAY1206 FINAL REPORT: AUDIO
PROCESSOR FOR TELEVISION
I O W A S TA TE U N I V E R S I T Y
SENIOR DESIGN
CLIENT
Texas Instruments
FACULTY ADVISOR
Dr. Randall Geiger
TEAM MEMBERS
Matthew Rench
Morgan Hodge
Max Jablonski
Xuetong Mao
Brian Joyce
TABLE OF CONTENTS
Executive Summary ................................................................................................................................................................ 3
Problem Statement ................................................................................................................................................................. 3
Concept Sketch ......................................................................................................................................................................... 3
Operating Environment ........................................................................................................................................................ 4
Intended Use and Intended Users..................................................................................................................................... 4
Assumptions .............................................................................................................................................................................. 5
Deliverables ............................................................................................................................................................................... 5
Approach Used.......................................................................................................................................................................... 6
Requirements Statement ................................................................................................................................................. 6
Functional Requirements ................................................................................................................................................ 6
Non-Functional Requirements ...................................................................................................................................... 6
Design Constraints ............................................................................................................................................................. 6
Market/Literature .............................................................................................................................................................. 7
Technical Approach ........................................................................................................................................................... 7
Testing Approach.............................................................................................................................................................. 11
Resource Requirements...................................................................................................................................................... 12
Detailed Design....................................................................................................................................................................... 13
Circuit Overview ............................................................................................................................................................... 13
Voltage Controlled Amplifier ....................................................................................................................................... 14
Peak Detector ..................................................................................................................................................................... 15
Differential Amplifier ...................................................................................................................................................... 16
Integrator ............................................................................................................................................................................. 16
Project Schedule..................................................................................................................................................................... 17
Work Breakdown.............................................................................................................................................................. 19
Expenses ............................................................................................................................................................................... 19
Implementation ...................................................................................................................................................................... 20
Standards .................................................................................................................................................................................. 21
Testing........................................................................................................................................................................................ 22
Blind Testing ....................................................................................................................................................................... 22
Tested Circuit Performance.......................................................................................................................................... 23
Additional Improvements .................................................................................................................................................. 26
Conclusion ................................................................................................................................................................................ 26
Appendix ................................................................................................................................................................................... 27
Operating Manual ............................................................................................................................................................. 27
References ................................................................................................................................................................................ 28
2
EXECUTIVE SUMMARY
With the advent of television, commercials have become an important market, playing a role in the
communications field. The purpose of commercials is mostly propagation of products, people, or a
particular event. However, in fulfilling the advertiser’s own goals, commercials are also producing
various inconveniences to consumers’ daily lives. It can’t be denied that viewers are, to some degree,
negatively affected by commercial content.
This audio processor aims to create a friendly and healthy environment for people watching TV programs
by leveling the volumes of those commercials which are much higher than TV programs (‘annoying’). Its
purpose is to make the audio signal stay in a stable range, to ultimately make transitions between regular
TV programming and commercials less noticeable.
PROBLEM STATEMENT
Cable TV channels frequently and intentionally increase the audio level of commercial content to garner
attention. This is an annoyance to consumers, and they wish for a solution. While some TVs include
audio processing to mitigate this problem, it is believed improvements can be made. The objective of this
project is to develop a prototype audio processor with amplitude-leveling capability. According to the
requirements, the implementation could be analog, digital, or any combination between.
CONCEPT SKETCH
In a specific use case, the device is connected between the television and the receiver of the speakers
using RCA cords. The setup is shown below in Figure 1.
FIGURE 1. USE OF DEVICE CONCEPT SKETCH
3
The device targets commercials that have higher average peak amplitudes than the television program, as
seen in Figure 2. The device will then adjust the gain of the signals to create more level amplitudes.
FIGURE 2. MODIFICATION OF SIGNAL
OPERATING ENVIRONMENT
Users that purchase the device will be people who care about the television ‘experience’. They are
annoyed by commercials and have actively sought a solution. Therefore, the device is expected to be
used with high quality audio speakers and equipment in addition to the standard TV speakers. The device
will need to be able to limit the unwanted distortion so it can be used with all ranges of audio equipment
from high end to low end.
In order to be used, the device will be paired with a TV at all times. It is expected that it can be used
anywhere television streams are watched. This means the device will be indoors or weather protected with
access to an AC power source. Thus, running on battery power or weatherproofing will not be addressed.
It will be assumed that the humidity is in the range of 20%-60%, and the temperature is in the range of
68-76 °F.
INTENDED USE AND INT ENDED USERS
The intended use of the product is to level the volume of ‘annoying’ commercials, those that affect the
comfort of the daily consumer. The unit must function together with TV sets and audio systems.
Installation will be the only major part of user interaction of this device. The device will have a set of
RCA audio inputs and outputs. The television audio will be connected to the inputs, and the user’s sound
system will be connected to the audio output.
The control for the system will consist of an on/off switch on the device as well as two additional
parameters that will allow the user to personalize the performance of the device.
During operation, the device will function automatically. One of the goals of the device is to allow the
user to become more immersed in the television program without being annoyed by commercials.
Therefore, the device will function for the majority of the time without needing any user input.
4
ASSUMPTIONS




There will be a 120V AC power outlet available.
Television / sound system will have external RCA outputs available to connect the device.
Users will have access to the device once installed to change the options.
Sound out of the device will be played over speakers that don’t apply a load (unlike headphones)
DELIVERABLES
The final design is an operating prototype of an audio processor with amplitude-leveling capability. It will
be an analog circuit that will have practical inputs and outputs allowing for various types of signals to be
passed through to speakers.
Once constructed, the prototype is tested against the design document to ensure it meets all of the given
constraints and has all the necessary features. The operating prototype is used to perform blind listening
tests.
5
APPROACH USED
REQUIREMENTS
The audio leveling device is developed for stabilizing the volume of the commercials relative to the
television program to allow the customers to enjoy consistent volume levels for all the viewing duration.
In other words, the device will make commercials less annoying.
FUNCTIONAL REQUIREMENTS







Input and output audio signals using RCA stereo cables
Output audio signal sounds more desirable than input
o Judged by a poll of potential consumers
Control the output to be either the processed or original signal
Adjust the maximum gain to the modified signal
Minimize the distortion in the output signal
o Audio delay is less than 45 ms
o Frequency distortion is less than 5dB for audible range
o Noise amplification is less that -30dB of white noise compared to content
Make length/width/height of the device a reasonable range so it can be easily carried inside a
room and easily connected to televisions
The operating environment should be between 32o-104oF
NON-FUNCTIONAL REQUIREMENTS
Legal and Regulatory Requirements:
Before the device is put into the market, it should have passed relative quality and legality
test or certification. However, this audio leveling device, solely being a proof of concept,
does not need to meet these requirements.
Physical Requirements:
The device should be encased in a durable shell to avoid being affected by the outside
environment or accidental damage. It should be portable, and safe for the user to operate.
DESIGN CONSTRAINTS
The device will be active during TV content as well as during commercials. Because of this, the
unwanted distortion that the device introduces during a TV program must be minimized.
In order to simplify the design, only the TV audio will be processed by the device. This means that a
large processing delay in the system will cause a de-synchronization of the video and audio signal. To
mitigate this, the device will delay the audio signal by less than 45 milliseconds. According to Advanced
Television Systems Committee, a delay less than 45 milliseconds is unable to be detected by the human
ear. i Additionally the device needs to limit frequency distortion. Excessive frequency distortion will
cause television programming to sound muffled or tinny. This is distracting and will take away from TV
content. The device will limit the frequency distortion to less than 5dB. This is less than frequency
distortion introduced by a high quality speaker system. ii
6
Finally, the signal noise will not be amplified. If the signal noise gets amplified, there could be cracking
or hissing present in the signal. The device should not amplify white noise to be greater than 30dB. This
is the amount of white noise found in un-altered TV programming.
MARKET/LITERATURE
The customer base for a device similar to this project is quite large; almost everyone is annoyed by loud
commercials at one point or another. There are a few options already on the market that target a similar
customer base. Three competing products were purchased and observed.
The first technology that resembles this problem’s potential solution is Dolby Volume. This is a processor
that can be put in a standalone device or integrated inside a television. It debuted in 2008, and has been
quite successful, so this shows there is a profit to be made with this sort of technology. The Dolby
Volume technology is used in an external device called the GefenTV Auto Volume Stabilizer. The
advertisement for this product states, “The GefenTV Auto Volume Stabilizer product is a high-quality
volume stabilizer. It actually makes the volume adjustments in such a subtle way that you won't even
notice the change.”iii This product uses an analog audio RCA cable.
SRS Labs is another company that has produced a similar but cheaper product. Like Dolby Volume, SRS
Labs has the option of integrating the technology into a television as well as an external device. Brands
already featuring this technology include: Dish Network, EchoStar, Philips, Samsung, Vizio,
Numbericable, and NXP. The technology is advertised to “provide the listener with a comfortable and
consistent volume level…The listener chooses the preferred volume level once and can rest assured it will
remain constant.”iv SRS Labs offers this technology in two external devices; one with a HDMI cable
connection and the other with an analog connection.
The third product found that resembles this project is the Terk VR1 Automatic TV Volume Controller.
This is a lower quality and less expensive device than the Dolby Volume and SRS Labs. The Terk is an
external device that is connected from the receiver to the television with RCA connectors. It is describe
as “a fully automatic device that automatically adjusts loudness to proper listening levels.”v
The CALM (Commercial Advertisement Loudness Mitigation) Act, signed by President Obama on
December 15, 2010, requires broadcasters to install technology ensuring commercials air at a volume no
louder than the programs in which they appear. However, this does not translate to an elimination of
annoying commercials. If a commercial is aired at the maximum loudness of the program in which it
appears, this does not mean that the content directly preceding the commercial was at maximum volume.
Large amplitude jumps can still occur, proving a continued need for the designed device.
TECHNICAL APPROACH
The approach used for the initial design decisions was very research intensive. Several hours of television
programming were recorded for analysis of the methods advertisers use to get people’s attention. In order
to develop a method of counteracting the annoyance factor of a commercial signal, knowledge of what
objectively makes a commercial irritating is necessary. Low amplitude signals followed by signals with
overall higher amplitudes and sharp transitions were two of the main characteristics found that describe
annoying signals.
According to the research, there are generally two ways to process an audio signal to reduce amplitudes:
automatic gain controller and dynamic range compression. The automatic gain control will alter the signal
similar to Figure 3. The circuit will change the amount of gain to make the amplitude of the signal lower.
The dynamic range compression will act as Figure 4. Once the amplitude reaches a certain trigger point,
7
the device will compress the signal and lower the amplitude. An ideal compression would have zero gain
after this point; however, it will also introduce a significant amount of distortion.
Both methods have advantages and disadvantages. When applying an automatic gain control, very little
distortion is introduced to the signal; however, quieter sounds will also be affected which could result in
unheard noises. For example, a whisper may not be heard, but a loud bang would be reduced. Using
compression will insure all quiet sounds are heard, but louder noises, such as someone yelling, could be
heavily distorted since it is altering the shape of the signal.
For this project, an automatic gain control circuit was chosen; however, it is only activated once a
threshold voltage is reached, eliminating the amplification of noise.
Automatic Gain Control
30
25
Amplitude
20
15
Origianal
10
Altered
5
0
1
2
3
4
5
6
7
8
9 10 11 12 13
FIGURE 3. CHARACTERISTICS OF THE AUTOMATIC GAIN CONTROL
Compression
30
Amplitude
25
20
15
Original
10
Altered
5
0
1
2
3
4
5
6
7
8
9 10 11 12 13
FIGURE 4. CHARACTERISITCS OF DYNAMIC RANGE COMPRESSION
There are also several devices in existence that are very similar to the proposed design. To ensure the best
available design is created, three competing products were purchased and run through a series of tests.
This was a very important step in the research since the results will show pre-existing design possibilities,
and allow a comparison for the final prototype device.
8
To determine which of the competing devices sound the best, several commercial signals were run
through them and then jumbled to make the test blind and fair. Group members then listened to the
unlabeled signals and rated the signals from best to worst. The results were compiled and can be seen in
the pie charts in Figure 5-7. The SRS compressor was the clear winner, which is surprising considering
the Gefen is the most expensive and uses the Dolby Volume technology that can also be found in many
high-end television sets in the market. The Gefen did fair moderately, being chosen as mid-range in
quality a majority of the time. It can clearly be seen that the Terk is not a favorable device, as it often
made the audio signals more annoying, and was consistently rated the worst processor.
Gefen
Best
Mid
Worst
FIGURE 5. BLIND TEST RESULTS FOR GEFEN AUDIO PROCESSOR
SRS
Best
Mid
Worst
FIGURE 6. BLIND TEST RESULTS FOR SRS AUDIO PROCESSOR
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Terk
Best
Mid
Worst
FIGURE 7. BLIND TEST RESULTS FOR TERK AUDIO PROCESSOR
From additional test results of the competitive devices, parameters that made the signal sound more
desirable were extracted. These parameters were used as the foundation of the circuit design. The gain
characteristics of the three devices are shown in Figure 8. From these plots, the knee points at which the
device starts altering the signal were observed as well the slope characteristics. In the Gefen (top),
amplitudes above .1V were kept at a constant gain, leaving the range of the automatic gain controller to
be less than .1V. The SRS (middle) modifies the gain of the signal to potentially always have a constant
output level for amplitudes above .2V. Amplitudes less than .2V are unmodified. The Terk (bottom)
performs similarly to the SRS but the gain increases for amplitudes less than .1V.
FIGURE 8. GAIN CHARACTERISTICS OF THREE COMPETIVE DEVICES
10
The transient responses of the devices were also observed by running a series of pulses through each
device. The results are shown in Figure 9 by showing the RMS value of the amplitudes with the original
signal shown on top. The Gefen (second) contains a slow settling time, resulting in the “swooping”
characteristic. The SRS (third) has a faster settling time but no other unique characteristics. The Terk
(bottom) also has a fast settling time, but occasionally will overshoot as seen on the fourth pulse.
FIGURE 9. TRANSIENT RESPONSE OF THREE COMPETIVE DEVICES
TESTING APPROACH
As previously mentioned in the Technical Approach, a survey of devices trying to accomplish feats
similar to this project will give comparable results for the final testable device. This is essential in the
final evaluation. Additionally, testing devices from other companies gives a reliable template for testing
the final prototype. It also gives a solid foundation of data to compare to the end device.
Testing is the most crucial part of this project. Since it is one hundred percent subjective, if people think
the signal sounds good, then it is a successful test. A blind test is set up on the project website to allow for
a large sample population. A signal processed through our device is compared against the same signal
processed through one of the competitive devices or the control signal. With a large enough sample
group, enough data is obtained to have a full comparisons of our device.
11
FIGURE 10. BLIND TEST LOGIC
To make sure all of the functional requirements are met, the delay of the system, frequency distortion, and
noise amplification are measured in the same way used on the competitive devices.
RESOURCE REQUIREMENTS






Access to information regarding commercial audio techniques
o This includes the internet and journal articles on audio manipulation
Information regarding completive devices
o Limited information is publically available through the manufacture’s website, alternative
methods need to be identified such as purchase and reverse engineering of two or three
competitors.
Access and ability to record TV streams including audio and video
o Importing audio streams into Matlab or some other audio processing software, such as
Audacity, to evaluate and test different techniques is needed.
Audio processing programs (Audacity)
o Once the audio streams have been recorded, they need to be imported into Audacity so
the characteristics of the signals may be evaluated. The application of different design
aspects should be tested in the software so potential solutions can be evaluated without
implementation.
Integrated circuits to implement the design
o Analog parts such as op amps, JFETS, resistors, etc. are needed to execute the design in
real-time to perform blind testing and evaluate the effectiveness.
A sample of blind test subjects to participate in trials
o A large group of participants is needed to obtain a statistically significant estimate of the
effectiveness of the product. A good sample group would represent a wide range of ages,
as well as technological backgrounds.
 A quiet environment where blind testing can take place without being corrupted by external
noises
12
DETAILED DESIGN
CIRCUIT OVERVIEW
The TV audio signal is input to a voltage controlled amplifier that is controlled by a feedback loop
containing a peak detector and integrator. The peak detector detects the low level of the audio wave as a
DC voltage. This voltage is then compared to a desired reference voltage, 1V in this case, and outputs a
DC voltage of the difference. The voltage is then integrated which turns the DC voltage into an increasing
or decreasing ramp that depends on the sign of the DC voltage from the differential amplifier. This is the
signal that controls a JFET in the voltage controlled amplifier that adjusts the overall gain of the system
accordingly.
FIGURE 11. CIRCUIT BLOCK DIAGRAM
13
VOLTAGE CONTROLLED AMPLIFIER
Both the first and the last steps in the circuit are the voltage controlled amplifier. Because the RCA
protocol uses stereo signals, the left and right signal paths must be kept separate but identical. The
voltage controlled amplifier has three separate stages.
10kΏ
Input Audio
Signal
10kΏ
Output Audio
Signal
1kΏ
1kΏ
Output to
Peak Detector
Input
Integrator
10x Attenuation
Variable Amplification
10x Gain
FIGURE 12. SCHEMATIC OF VOLTAGE CONTROLLED AMPLIFIER
First, there is a 10x attenuation to reduce the input signal from a 2Vpp range signal down to 0.2Vpp. This
is necessary because the input voltage is also applied over the drain and source of the JFET. Therefore, a
small signal is needed to keep the JFET in the linear region. If the JFET is not in the linear region,
distortion is introduced in the signal. This attenuation is done through a resistive network.
The next stage is the variable amplification stage. This stage is a non-inverting amplifier where
𝑅𝑙
𝑉𝑓𝑒𝑡 = 𝑉𝑖𝑛 ∗ (1 + 𝑅𝑓𝑒𝑡) where Rl is the user controlled low potentiometer.
The value of Rfet is
controlled by the feedback loop to adjust the gain of the amplifier to make the output at the desired level.
As the gate voltage of the JFET changes from 0V to -3V, the resistance of the JFET changes from 30Ώ to
over 1kΏ. This allows the gain of the amplifier to change from 6 to about 1 as needed. The gate voltage
comes in from the feedback loop. This part of the circuit is also where the cutoff is determined. Since the
maximum value of Rfet is fixed by the feedback loop, changing Rl will control where the circuit stops
increasing the gain. This sets the low cut point for the amplifier. However, if the low cut threshold has
not been reached, this amplifier increases the signal amplitude so that it matches the set desired level.
Because the left and right signal paths should be the same, the Rl and Rfet are the same for both paths.
After the variable amplification stage, the signal is fed into a simple 10x gain amplifier to get the signal
back in the 2Vpp maximum range. This signal is the final output, and it is the input to the feedback loop
which begins with the peak detector.
14
PEAK DETECTOR
The peak detector circuit also has three stages; a summing circuit to convert the left and right ears into a
single, a full wave rectifier, and peak detector.
Input from 10kΏ
Left Ear
Input from
Right Ear 10kΏ
1kΏ
5kΏ
1kΏ
1kΏ
1kΏ
3.3kΏ
1kΏ
Summer
Full Wave Rectifier
Output to
Differential Amp.
1MΏ
1uF
Peak Detector
FIGURE 13. SCHEMATIC OF PEAK DETECTOR
Because both the right and left ear signal paths have the same gain, there should only be 1 peak detected
between both ears. For this reason, the first step in the peak detector is a weighed summing circuit. This
circuit adds the left ear signal and the right ear signal together, and then attenuates by 2. The resulting
signal can be used to detect the overall loudness of both channels.
The output of the summer is fed into a precision full wave negative rectifier. This is built from two
amplifiers; the first amplifier inverts the positive half of the wave and the second amplifier adds this
signal to the already negative part. A full wave rectifier was used instead of a half wave rectifier because
a full wave rectifier cuts the potential response time in half. It also marginally improves accuracy since a
singular, loud, positive peak would be missed with a half wave rectifier. The rectified wave feeds into the
detection system.
The detection circuit is a voltage follower amplifier that is put into a capacitor circuit to store the value.
The capacitor has resistances in series that limit how fast it charges and discharges. The capacitor time
constant can be computed by multiplying the resistance value by the capacitance value, T=RC. Since R
can be controlled by the user, this is where the time response parameter can be controlled. There is also a
resistor in parallel with the capacitor which allows the capacitor to discharge. This means the value of the
peak detector fades over time. The end result is a representation of the loudness of the audio as it changes
over time.
This is compared to the desired loudness in the differential amplifier.
15
DIFFERENTIAL AMPLIFIER
1kΏ
Input from peak detector
1kΏ
Output to integrator
Desired voltage input
1kΏ
1kΏ
Differential Amplifier
FIGURE 14. SCHEMATIC OF DIFFERENTIAL AMPLIFIER
The differential amplifier is an important part of the circuit. It is used to compare the output of the peak
detector circuit to a desired value. Since the peak detector is slowly changing and the reference voltage is
DC, the output is a DC voltage equal to the signal level subtracted from the desired voltage level. This
output is sent to the integrator.
INTEGRATOR
10nF
680kΏ
1kΏ
Input from differential amplifier
1kΏ
Output to voltage controlled amplifier
-1V
1kΏ
Integrator
1kΏ
Biasing Differential Amp.
FIGURE 15. SCHEMATIC OF INTEGRATOR
The integrator circuit is the key to getting the desired output level. First, the integrator receives a DC
voltage from the differential amplifier circuit. This voltage will either be positive or negative depending
on whether the signal is too loud or too quiet. With this type of input, the integrator’s output will either
−1
ramp up or down depending on the sign of the input and with a slope of 𝑅𝐶 𝑉𝑖𝑛 . Since the peak detector
was used to control the time constants on how fast the circuit responded, the RC time constant here is set
to insure the integrator responds faster than the peak detector. This allows the peak detector to be the
driving force in circuit response time.
16
Additionally, if there is a Vin=0, meaning the peak detector output matches the desired level, there will be
no change in the output. This signal can be used as the controller for the JFET. The initial conditions on
the capacitor are zero, so to put our device in the desired initial circuit gain, a differential amplifier is used
to bias the integrator output to -1V.
Overall, the circuit works in the following way:
The audio signal goes small, the peak detector value will go low, making the output of the differential
amplifier go high and ramp down the integrator’s voltage. As the differential amplifier’s voltage ramps
down, the resistance of the JFET increases which also increases the gain of the variable amplifier. This
then increases the amplitude of the output until it matches the desired level. When the amplitude matches
the desired level, the output of the differential amplifier goes to zero which makes the integrator hold its
current value. This then ultimately makes the gain of the variable amplifier constant. Until the audio input
signal changes levels again, the process repeats.
PROJECT SCHEDULE
To keep the team organized and driven, milestones were established in a Gantt chart format. This allowed
members to easily see where a given task stood, where it was in terms of date, and to what degree it has
been completed. Microsoft Project can be used to gradually change the completion rate of a job, allowing
for an easy showcase of where the group itself stands, and if more time needs to be spent on a task to
ensure it is completed.
The layout for the schedule of the first and second semester of the project is shown below in Figures 16
and 17. The first semester focused on defining the project by researching characteristics of annoying
signals and solutions that would address all of these characteristics. The second semester then focused on
designing and implementing a solution to the main offending characteristics because time did not allow
all solutions to be addressed.
17
FIGURE 16. FIRST SEMESTER GANNTT CHART OF SCHEDULE
FIGURE 17. SECOND SEMESTER GANNTT CHART OF SCHEDULE
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WORK BREAKDOWN
The breakdown of each team member’s contribution for of the project is summarized in Table 1.
TABLE 1. WORK BREAKDOWN SUMMARY
Competitive Research Programming Website Recordings Presentations Meetings Design Total
Team
Documents
Devices
Member
Max
12
17
18
2
1
12
7
70
20
159
10
18
2
1
15
7
70
20
160
Morgan
17
Matt
18
10
15
2
30
6
7
70
5
163
Brian
Amy
Total
17
11
75
13
8
58
13
18
82
21
11
38
2
1
35
7
5
45
5
7
33
70
70
350
40
20
105
188
151
821
EXPENSES
The anticipated cost stated in the proposal for this project is $400. A total of $349.56 has been spent on
the three competing devices, audio cables, and circuit parts to implement the circuit design. A TV tuner
card was also purchased to obtain a large sample of signals.
TABLE 2. TOTAL EXPENSES
Price Breakdown
Cost
Competitive Devices
Terk Audiovox
$25.54
GefenTV
$177.50
SRS
$47.99
Recording
Hauppage TV Tuner
Audio Cables
$49.99
$9.99
Implementation
Potentiometers
Power Supply
RCA Connectors
Project Box
$11.92
$10.63
$9.00
$7.00
Total
$349.56
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IMPLEMENTATION
The circuit was first implemented on a bread board during the design phase on a test bench. Once the final
design was reached, the parts were then soldered on a perforated prototype board. RCA connectors,
potentiometers, and power connectors were bought and implemented into the soldered board. A plastic
box was then placed over the board to protect it from the environment and keep the users safe.
FIGURE 18. OVERALL SCHEMATIC OF CIRCUIT DESIGN
FIGURE 19. SOLDERED CIRCUIT BOARD
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STANDARDS
In this designed system, the only interference with an already existing system is through RCA cables and
into the speaker system. Because of this, the designed system needs to be compatible with both of these
standards.
RCA CABLES
CABLE SPECIFICATIONS
Core Configuration
Conductor Size
Ov. Jacket
Material
Ov. Dia.(mm)
2×75 ohm Coax.
0.126mm² (AWG#27)
Flexible PVC
2×3.0Ø(0.118")
Color
Black
ELECTRICAL & MECHANICAL CHARACTERISTICS
DC Resistance at 20°C
Inner Cond.
0.15ohm/m (0.046ohm/Ft)
Shield
0.04ohm/m (0.012ohm/Ft)
Capacitance at 1kHz, 20°C
59pF/m(16.8pF/Ft)
Characteristic Impedance at 10MHz
75 ohm±5%
Attenuation (10MHz)
0.007neper/m (0.0021neper/Ft)
Phase Constant (10MHz)
0.28rad/m
Electromagnetic Noise*
0.1mV Max.
Voltage Breakdown
Must Withstand at DC 500V/15sec.
Insulation Resistance
1000000Mohm × m Min. at DC 500V, 20°C
Flex Life*
24,000 cycles
Tensile Strength
40kg
Emigration
Non-Emigrant to ABS resin
Applicable Temperature
Standard
-20°C~+60°C (-4°F~+140°F)
UL Subject 758 AWM 2552 VW-1 60°C 30V, -F-
Maximum temp. rating 60C (140F). Maximum voltage 30V Suitable for Class 2 wiring of electrical equipment.
*Attenuation: 1 dB=0.1151 neper (1 neper=8.686 dB)
*Using standard testing methods.
SPEAKERS
The input level of the speakers varies between different brands. The output range of the designed device
should be between –1V and 1V. This will be ensured by latching the output to stay in the range. However,
this feature will be implemented in future revisions. Once this feature is implemented, the designed
device will be compatible with all speaker input levels.
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TESTING
As stated in the Testing Approach, the device performance was tested by conducting a blind test as well
as calculating the delay, distortion introduced, noise amplification, and gain and transient characteristics.
BLIND TESTING
From an online poll set up on the project’s website, statistical information was collected determining if
the output signal sounded more pleasant than the original and the other competitive devices. Fellow senior
design students as well as family and friends were asked to participant in the survey by answering the
questions shown in Figure 20 on the website. Each participant was given a different grouping of signals
by randomizing the signal played against the designed device.
FIGURE 20. SCREENSHOT OF ONLINE POLL
The participants then listened to the two signals in each poll and pick which signal sounds more
annoying. The data was recorded and summarized in Table 3. The total number of times the signal was
picked to be more annoying is shown in the 2nd column. In all cases, the designed device was chosen to be
the better sounding signal more times than the opponent.
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TABLE 3. BLIND TEST RESULTS
Designed Device vs Original
Original
Designed Device
Total
8
1
Designed Device vs Terk Audiovox
Terk Audiovox
Designed Device
11
8
Designed Device vs Gefen
Gefen
Designed Device
13
11
Desgined Device vs SRS
SRS
Designed Device
17
5
Approximately 25 participants took part in the online poll and each listened to 3 sets of signals. By using
a confidence interval analysis, it can be concluded with a 99% confidence interval that the designed
device will be picked 59% to 73% of the time for being the better sounding signal.
TESTED CIRCUIT PERFORMANCE
To determine if the device is working as expected and meets the requirements, various characteristics
were observed through similar tests that were used on the competitive devices.
To determine the steady state gain characteristics, varying voltage level signals were applied to the input,
and the output voltage level was recorded. Figure 21 displays Vin plotted against the gain, Vout/Vin. For
already quiet signals, the gain is unchanged. In this way, any static or back-ground noise is not amplified
into the circuit. Once the TV audio input exceeds a threshold loudness, the gain is decreased to keep the
output amplitude constant.
FIGURE 21. STEADY STATE GAIN CHARACTERISTICS OF DESIGNED DEVICE
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The transient response was also measured by looking at a signal with rapidly-changing amplitudes, shown
in Figure 22. Different sweeps of white noise were run through the device, simulating how the circuit will
respond to real-world broadcast signals. From this, the settling time was measured by changing the
amplitude of the input signal and measuring the time it took for the output to settle at the corresponding
level. This value was measured to be 40ms.
FIGURE 22. TRANSIENT RESPONSE OF DESIGNED DEVICE
The distortion the device introduces into the signal was measured by running a signal of white noise
through the device and observing the response. The analysis of the response was done by taking the
Fourier transform of the output signal and observing the frequency versus amplitude in dB relationship.
As seen in Figure 23, very little is distortion is introduced until around 20kHz which happens to be the
high end limit of the hearing range to humans. For frequencies in the audible range of less than 20kHz,
the device meets the function requirement of having less than 5dB of frequency distortion.
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FIGURE 23. DISTORTION INTRODUCED FROM DEVICE
To determine if the device satisfies the function requirement of having less than -30db of noise
amplification, a signal made of 5 different frequencies was ran through the device and analyzed with a
Fourier transform. From Figure 24, it can be seen that for the entire signal, the noise amplification is
always less than -30db.
FIGURE 24. TEST TO MEASURE NOISE AMPLIFICATION
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The delay of the system was measured by observing the output response of a changing input with an
oscilloscope. Figure 25 shows the screen shot of this measurement, and the delay is calculated by
observing how long it takes the output to reach the same level as the input. The delay was found to be
.4ms which is well within the function requirement of being less than 45ms.
FIGURE 25. OSCILLISCOPE SCREENSHOT OF MEASUREMENT OF DELAY
ADDITIONAL IMPROVEMENTS
The next step for the project would be to optimize the circuit design by using the least amount of
components as possible. Additional features could also be added including a wireless remote control, user
controls such as silencing the audio for a certain amount of time if a button is pressed, or integrating the
circuit inside of the television. The circuit can be improved by implementing a clamping circuit at the
output to ensure the voltage is never more than 2Vpp to protect speaker systems that may be attached.
In continuation of this project, the same functionality could be attempted using digital signal processing
instead of an analog circuit, or attempt to detect commercial transitions to allow a more aggressive
algorithm to be applied without affecting the TV programing.
CONCLUSION
The objective of this project was to design a prototype audio processor with amplitude leveling capability
that will make commercials less annoying. The first half of the project focused on researching annoying
characteristics to turn a subjective proposal into an objective problem. Once annoying signals were
defined, more research was done on solutions for each of these characteristics. The second half of the
project focused on only one of these solutions since time restricted design of all solutions. An analog
circuit was designed and implemented to perform automatic gain control on a signal to output a constant
level amplitude signal. A blind test was performed that statistically proved the signal ran through the
designed circuit sounds more pleasant than the original, as well as the competing products already on the
market.
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APPENDIX
OPERATING MANUAL
PANEL LAYOUT
1.
2.
3.
Bypass
Switch
Low Cut
Control
Time
Response
4.
Analog Input
5.
Analog Output
FIGURE 26. DEVICE LAYOUT
1.
2.
3.
4.
5.
Bypass Switch
Low Cut Control
Time Response
Analog L/R (RCA) Inputs
Analog L/R (RCA) Outputs
CONNECT INTO TV STYSTEM
Insert RCA cables from the audio source into the Audio Input jacks on the device (3).
Use the second set of RCA cables to connect the Audio Output (4) jacks to the receiver/audio system
input.
Make sure the light next the Bypass switch is off, otherwise press the Bypass switch.
CONNECT POWER SUPPLY TO WALL
Connect the provided 20V power adapter to the power receptacle.
USER CONTROLS
Bypass: If the user wishes to turn off the device, push the bypass switch to output an unaltered signal.
Low Cut: If the user wishes to set the low level where the device will begin to modify the amplitude of
the signal, adjust this knob. This control allows the user to make small adjustments to eliminate noise.
Time Response: This knob will modify the circuit’s reaction time to changes in the input amplitude. If
annoying transitions are audible, the response can be adjusted to the user’s liking.
27
REFERENCES
"ATSC Implementation Subcommittee Finding: Relative Timing of Sound and Vision for Broadcast
Operations Advanced Television." ATSC Implementation Subcommittee Finding: Relative Timing of Sound and
Vision for Broadcast Operations (2003). Advanced Television Systems Committee. Web.
<http://www.atsc.org/cms/standards/is_191.pdf>.
i
ii
“MR5mk2: Owner’s Manual,” http://www.mackie.com/products/mrmk2series/pdf/mr5mk2_om.pdf.
"GefenTV Auto Volume Stabilizer." Gefen, LLC. Web. 31 Oct. 2011.
<http://www.gefen.com/kvm/dproduct.jsp?prod_id=8707>.
iii
"TruVolume." SRS Labs: Solutions. Web. 31 Oct. 2011.
<http://www.srslabs.com/content.aspx?id=1953>
iv
"Terk VR1 Automatic TV Volume Controller." Amazon.com: Online Shopping for Electronics, Apparel,
Computers, Books, DVDs & More. Web. 31 Oct. 2011.
<http://www.amazon.com/Terk-VR1-Automatic-TV-ontroller/dp/B00008VWOJ/ref=sr_1_1?s=electronics>.
v
“Technical Specs of Component Video Cable.”
<http://www.svideo.com/mogami3spec.html>
V
28