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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[Fig. 50] All-pass level and band levels
Please note that it is NOT the right way to determine the playback level of the speakers only from the all-
pass level. [Fig. 51] is an example showing the response of two types of pink noise whose all-pass level is
85 dBC. The black shows the response of 20 Hz - 20 kHz broad-band pink noise, and the grey shows the
response of 80 Hz - 8 kHz narrow-band pink noise.
[Fig. 51] Difference of the band level between the wide band pink nose and the narrow band pink noise
When the all-pass level is adjusted to the identical 85 dBC, the narrow-band pink noise has a higher band
level than the broad-band pink noise (71dB→72dB). This means that if the playback level is adjusted
referring only to the all-pass level for speakers with differing frequency ranges, differences in band level
will occur. For example, let us suppose that the front speakers are large speakers with a broad frequency
response, while speakers with a narrow frequency response are used for the surround channels. In such an
environment, relying only on the all-pass level (85 dBC) to adjust the playback level of those speakers
will mean that the playback band level of the surround speakers will be higher, and as a result, the
surround channels will play back at a louder volume than the front channels.
Matching the speaker playback levels means that the band levels (71 dB, 1/3 octave) — not the all-pass
level —must be matched. Adjustment based on the all-pass level (85 dBC) using only a sound level meter
is an easy method that is possible only if all speakers have the same playback response and the room
acoustics are sufficiently good. In actual measurement, it is desirable that you check not only the all-pass
level (85 dBC), but also use an RTA to check the band levels (71 dB, 1/3 octave).
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
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 frequenc
y
[Hz]
SPL [dB]
All pass level : 85dBC
1/3 octave band level : approx.71dB
Wide band
All pass level : 85dBC
1/3 octave band level : approx.72dB
Narrow band