Stereo and Surround Mixing
Techniques
Mixing Techniques
Broadcast Vs. Theatrical
The most significant difference between home and theatrical
mixes is the dynamic content of the mix.
Mixing for home viewing sometimes involves making
compromises in order to ensure that the mix translates to the
maximum amount of end users.
Primarily this involves raising the low parts so that they won’t
be lost in the high noise floor environment typically found in
the home.
Mixing Techniques
Broadcast Vs. Theatrical
Much of the detail work in dialogue editing is also more
apparent in the home environment due to 2 reasons.
- Audience’s proximity to the speakers
- No screen between the speakers and the audience
Mixing Techniques
Broadcast Vs. Theatrical
Delivery specs also differ between the 2, and different tools
are needed for to accomplish them for each.
A few typical television specs might be
-Content should be mixed in a properly calibrated
-Peak audio at -10dbfs
-Dialogue at -24lkfs +/-2db
-Overall Levels at -24lkfs +/-2db
-Average levels hovering around -20dbfs
-room
Mixing Techniques
Broadcast Metering
The Dolby Media Meter allows the engineer to monitor lkfs levels
which are becoming the de-facto spec for broadcasters.
The TC Electronic LM5 is also a viable option.
Broadcast engineers often use Dorrough meters as well. These
allow the engineer to monitor both peak level and average
loudness
Many “old school” engineers still like the feel of traditional vu
meters and use them as a reference though the dbv spec has
virtually disappeared.
Mixing Techniques
Theatrical Trailer or Commercial
-Content must be mixed in a properly calibrated studio
-No peak measurement
-Loudness must not break 86 Leq(m)
The Dolby Media Meter is capable of measuring Leq(m), but at
some point the audio will need to pass through Dolby’s DMU
for mastering and encoding which also measures Leq(m)
Mixing Techniques
Broadcast Vs. Theatrical
Film for Theatrical Release
-Content must be mixed in a properly calibrated studio
-There are no peak, average or Loudness
measurements
-Mixes are done to ear and then typically mastered on
Dolby DMU (for Dolby Print Mastering)
-The DMU also provides metering
-the
Mixing Techniques
Loudness
The hot topic of the moment in audio post seems to be the
idea of loudness, and its perception.
The Leq measurement is designed to measure loudness over
time.
Basically the measurements we discuss are based on this
concept. Each variation applies a different filter to their
loudness measurement and therefore yield different results.
Mixing Techniques
Loudness
Leq(m) for example is designed to be sensitive to the mid and
high frequencies that audiences in theatres might find
objectionable at high volumes.
Lkfs is the current loudness standard for television and stands
for Loudness K-weighted relative to Full Scale. This is often
measured with dialogue intelligence on which allows the meter
to measure only the dialogue loudness and gives the mixer the
ability to add dynamics through the other elements.
Mixing Techniques
Loudness
The CALM act was passed in on September 29th, 2010, and
mandates the maximum loudness in commercials not exceed
the average maximum loudness of the accompanying
programming.
The FCC must enforce this law within a year of its passing.
Mixing Techniques
Calibration
The process for calibrating a studio for theatrical mixing and
television mixing are similar.
Pink noise is used to calibrate SPL at the mix position.
For theatrical mixing pink noise ins generated from the mixing
platform (pro tools) at -20dbfs and output through one speaker
at a time. Each speaker is adjusted to read 85 dbspl at the mix
position.
Mixing Techniques
Calibration
For broadcast mixing, pink noise is generated from the mixing
platform (pro tools) at -20dbfs as well. In this situation each
speaker is adjusted to read 79 dbspl at the mix position.
What is the result of mixing on lower volume levels?
Mixing Techniques
Calibration
Studio size is also a concern.
It is recommended that you lower the dbspl reading at the mix
position as the proximity between the speakers and the mix
position increases.
So for smaller studios, films are recommended to be calibrated
at 79 db, and as low as 76 for broadcast.
Mixing Techniques
Calibration
The reason for this change is the psycho-acoustic effect
speaker proximity and room size has on the way we perceive
loudness.
Our perception of loudness increases as we get closer to a
sound source and as the space in which the sound is
perceived decreases.
Mixing Techniques
Subwoofer Calibration
Subwoofer calibration is a bit more murky and depends largely
on your specific system configuration.
In general the same rules apply to the sub as the main
channels. Some documents require filtered noise to be sent to
the sub and then measured, some require alignment 3-6db
lower than the other channels.
In theatrical applications a Real Time Analyzer is often used to
get a specific view of the frequency readings.
Mixing Techniques
Subwoofer Calibration
Consumer subwoofer setups very greatly and knowledge of
the concept of bass management and its principles is
important in order to create a good 5.1 mix.
Mixing Techniques
Starting the Mix
The session template is opened that is most appropriate. Many
engineers have one template capable of handling numerous
tasks.
As illustrated in the setup class the first step is loading the
OMF/AAF file.
Mixing Techniques
Starting the Mix
This file should load with proper handles in order to facilitate the
mixing process.
Handles allow each audio file to be trimmed out an additional predetermined amount of time.
For longer form projects sometimes handles up to 10 seconds are
considered standard, whereas for short form, many times 2
second handles are sufficient.
Increasing handle size will increase the file size of your
OMF/AAF.
Mixing Techniques
Starting the Mix
In order to ensure that all files are properly aligned it is
considered standard practice for the first frame of video to start at
1 hour.
The omf/aaf file should load so that the first frame of audio begins
at 01:00:00;00.
Many times video editors will add an arbitrary number of black
frames at the head of the video file.
The only way to ensure proper alignment is to load the audio from
the quicktime and line the audio from the video up to the audio
from the OMF/AAF
Mixing Techniques
Starting the Mix
The most foolproof method is to have the editor add a 2 pop in
the omf that corresponds to a flash from on the video.
The 2 pop is typically a 1 or 2 frame 1khz pop that starts
exactly 2 seconds before the first frame of video. By aligning
the pop with the flash frame we can assure proper sync.
Broadcast wave files also allow for time stamping which can
be useful for both sound engineers and video editors as the
time code location is embedded in the audio file as a form of
metadata.
Mixing Techniques
Stem Mixing
Once the initial editing phase of each stem is under-way the pre-mix
process begins.
Level, eq, compression and noise reduction choices are made.
Ideally we want our pre-mixes to have as little compression as possible
but still feel controlled.
Certain stems are capable of handling more compression than others.
The music stem tends to have less compression as a whole whereas the
effects stem may be more compressed.
In the end these are creative decisions that will define the sound of the
mix and will have to be made on a case by case basis.
Mixing Techniques
Mixing
If the project has had a number of people working
simultaneously on the different stems we must now bring the
elements together and find a way for them to inhabit the same
soundtrack.
Maintaining eq and dynamic control is the main way this is
achieved.
Mixing Techniques
Mixing
As we bring together these element we start to notice the
limitations of certain systems particularly while mixing in 5.1.
Decisions will have to be made about bussing architecture and
processing in order to maximize our systems.
Changing playback engine settings can often buy you more
dsp from the system.