User Manual
Multichannel Monitoring Tutorial Booklet (M2TB) rev. 3.5.2
Masataka Nakahara : SONA Corporation
©2005 YAMAHA Corporation, ©2005 SONA Corporation
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6-3. Narrow-band pink noise
We can consider the following factors as possible reasons for differences in frequency response between
playback channels.
1. Playback response of the speakers Playback limitations at the low and high ranges
2. Acoustical response of the room Inconsistent low-frequency response
In addition to the above, the results of adjustment can be affected by the margin of error in the
measurement system, such as:
3. Response of the sound level meter mic Inexpensive units are not able to measure the high-
frequency range
As described above, there is a close relationship between frequency response and the all-pass level. This means
that in an environment where there is inconsistency between the playback levels of each channel, it is possible
that major errors may occur if you make adjustments using only a sound level meter (all-pass level 85 dBC),
and that it is therefore desirable that you also use an RTA to check the band levels (71 dB, 1/3 octave).
If you suspect that there is inconsistency between the frequency response of the channels, but it is difficult
to make adjustments using an RTA, then you may be able to obtain good results in some cases by using
500 Hz - 2 kHz band-limited pink noise as the adjustment signal. The reason is that 500 Hz - 2 kHz band-
limited pink noise does not include the low-frequency region which often causes instability in the
frequency response of the playback environment, nor the high-frequency region which is easily affected
by the quality of the sound level meter.
[Fig. 52] shows the response of broad-band pink noise (black) and 500 Hz - 2 kHz band-limited pink noise
(gray). You can see that because the 500 Hz - 2 kHz band-limited pink noise has a narrower bandwidth than
the broad-band pink noise, its all-pass level is 80 dBC, which is 5 dB lower. Thus when using the 500 Hz - 2
kHz narrow-band pink noise to adjust the level of each channel, you must set the all-pass level (the value
indicated by the sound level meter) not to 85 dBC, but to 80 dBC which is 5 dB lower.
[Fig. 52] 500-2kHz Pinknoise and Broadband Pinknoise
Most of the pink noise built into consumer receivers and players is band-limited pink noise of this type.
However since its level is not precise, you must use caution when making adjustments targeted at an
absolute value such as 85 dBC or 80 dBC.
Some devices such as the Dolby Laboratories DP564 professional decoder have built-in band-limited pink
noise to which level compensation has already been applied, and in such cases, you can make adjustments
to 85 dBC (not 80 dBC) even when using band-limited pink noise.
40
50
60
70
80
90
AP(C)
20
31.5
50
80
125
200
315
500
800
1.25k
2k
3.15k
5k
8k
12.5k
20k
1/3 octave band center frequency [Hz]
SPL [dB]
All pass level : 85dBC
1/3 octave band level : approx.71dB
Wide band
All pass level : approx. 80dBC
1/3 octave band level : approx.71dB
500Hz-2kHz