Project: Comparison of the objective and the
subjective parameters of the different types of
microphone preamplifiers
Author: Michał Łuczyński1, Maciej Sabiniok2
1,2
Faculty of Electronics, Chair of Acoustics and Multimedia, Wroclaw University of Technology,
Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
1michal.luczynski@aes.pwr.edu.pl
2maciej.sabiniok@aes.pwr.edu.pl
Full manuscript:
Audio Engineering Society Convention Paper number 9550
140th AES Convention 2016 June 4-7 Paris, France
ABSTRACT
The aim of this paper is to compare different types of microphone preamplifiers. The authors designed 6 types of
preamps using different technologies (f.ex. based on vacuum tube, transistors, operational amplifiers). Assumed
parameters such as input signal, gain, power supply were the same for all circuits. Preamps were tested by objective
and subjective methods. Then authors tried to find out relations between different gain components, electroacoustic
parameters and subjective sensation. The authors did not mean to create commercial devices. Just to compare and
classify objective and subjective parameters depending on the different types of microphone preamplifier.
CIRCUITS
Figures from 1 to 6 shows electronic circuits of performed preamplifiers. Figure 7 shows the entire
device.
Figure 1 Electronic circuit of bipolar microphone preamplifier
Figure 2 Electronic circuit of field effect microphone preamplifier
Figure 3 Electronic circuit of hybrid microphone preamplifier
Figure 4 Electronic circuit of operation amplifier microphone preamplifier
Figure 5 Electronic circuit of SSM2019 microphone preamplifier
Figure 6 Electronic circuit of vacuum tube microphone preamplifier
Figure 7 Six channel microphone preamplifier
MEASUREMENTS
Objective method
In order to define electroacoustic parameters microphone preamplifier were tested at Audio Precision.
The tested parameters are: the level of noise, Signal to Noise Ratio, Total Harmonic Distortion plus
noise, frequency response and impulse response. Figure 8 shows measuring block diagram.
Figure 8 Measuring block diagram
Table 1 Electroacoustic parameters of tested preamplifiers
Preamp
bipolar
fet
hybrid
opamp
ssm
vacuum
gain
[dB]
40
40
40
40
40
40
THD+n[%] SNR [dB]
@ 10mV
@ G 100
0,044
0,050
0,018
0,020
0,014
0,100
SNR [dB]
@ 10mV @ max out
@ G 100
@ G 100
73,8
76,9
81,5
84,1
83,8
79,9
87,8
89,6
100,8
104,3
103,7
-
max out
[dBu]
16,2
15,3
21,8
22,2
33,1
-
Figures from 9 to 14 show frequency response of testing preamplifiers.
Figure 9 Frequency response of bipolar microphone preamplifier
Figure 10 Frequency response of field effect microphone preamplifier
Figure 11 Frequency response of hybrid microphone preamplifier
Figure 12 Frequency response of operational amplifier microphone preamplifier
Figure 13 Frequency response of SSM2019 microphone preamplifier
Figure 14 Frequency response of vacuum tube microphone preamplifier
Subjective method
In this paper subjective tests were carried out as two methods: matching pairs and parametric.
In listening test 30 listeners were attended. They were students studying at Wroclaw University of
Technology and their specialization – was an acoustics. All of them are actively engaged in Wrocław
student section of Audio Engineering Society. In order to ensure reliable testing condition the test
was divided into two parts. Before starting the regular test the learning test were done in order to
discussed the test parameters.
The test material was evaluated for the five parameters such as binary preferences method. The scale
of assessment is 1- poor, 2 – mediocre, 3 – satisfactory, 4 – good, 5 – very good.
Figure 15 shows block diagram of recording system setup.
Figure 15 Recording block diagram
Figure 16 to 18 show results obtained in subjective a binary preference test. Figure 19 to 21 show
results of test using a single presentation of music sample.
On the vertical axis there is an average rate in each category (parameters). On the horizontal axis
there are parameters (selectivity, brightness, spaciousness, dynamics and rate).
Figure 16 Result of the binary preferences test for guitar
Figure 17 Result of the binary preferences test for saxophone
Figure 18 Result of the binary preferences test for speech
Figure 19 Result of the parametric test for guitar
Figure 20 Result of the parametric test for saxophone
Figure 21 Result of the parametric test for speech
Figure 22 shows average rate of each preamplifiers for parametric test (regardless of sound sources).
On the graph there are marked standard deviations of whole results for each parameters in the
parametric test.
Figure 22 Average rate of each preamplifiers (regardless of sound sources)
CONCLUSIONS
The great influence to the subjective assessment has the type of sound source.
Even very low differences in THD and SNR parameters could have impact to assessment of
preamplifiers. However an investigation an influence the level of this parameters to listeners
impressions isn’t the aim of this paper.
In general the differences between each preamplifiers was very subtle but audible for sound engineers.
The most important factor is personal preferences. The Authors encourage to listen the sample on
themselves. All sample are available on http://www.aes.pwr.edu.pl/projects.