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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6-5. Delay adjustments
Even in an environment in which all speakers are placed at an equal distance from the listening point, it is
best to measure and adjust the time alignment. In addition to differences in the distance to each speaker,
the time at which the playback sound arrives can often be delayed slightly by the electrical rigidity of the
individual speaker, other materials, or wiring, and monitoring problems such as impaired highs can occur
due to these reasons.
For time alignment adjustments, the first step is to apply a delay based on the differences in the distance
to each speaker. Whether the distance difference is calculated based on the distance difference within the
horizontal plane or the actual distance difference will depend on how the surround sound field and the
playback response affect each other (see p.47, section 3-8-4).
or
* [msec] = millisecond (1/1000th of a second)
Next, check whether any comb filtering effects are occurring due to slight time differences between
channels.
Play back the same pink noise at the same timing from the two channels being adjusted, and use an RTA
to check the frequency response.
If dips that were not seen for the individual channels occur when the two channels are played back
simultaneously, it is possible that a comb filter effect is occurring due to differences in delay.
[Fig. 56] Time alignment using an RTA: checking for comb filtering
[Fig. 56] shows an example in which dips not seen in channel A or channel B occur at 12.5 kHz when
channels A and B are played back together.
In this case, this means that there is a playback difference of approximately 0.04 msec between channel A
and channel B. 0.04 msec corresponds to a difference of approximately 14 mm in difference. If you notice
a dip caused by this type of comb filtering effect, adjust the delay between channels so that the dip is
shifted to a frequency higher than the audible limit of 20 kHz. If dips are not seen in the region below 20
kHz, this means that the two channels are time-aligned with a precision of 0.025 (8 mm) msec or better.
If a highly correlated signal is reproduced from two speakers from which comb filtering effects have not
been eliminated, such as in [Fig. 56], a loss of highs will be perceived in the playback sound at the
listening point. This is a particularly important problem in a playback environment for musical material
that uses signals that are highly correlated between differing channels in an attempt to reproduce precise
sound field expressions.
40
50
60
70
80
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]
Channel A
A+B
Channel B
Difference
0.025
0.06
0.130.25
0.5
1.0
9
22
43
86172
344
[msec]
Comb filtering effect
90
[mm]
Delay time [msec] =
Sound speed; 344 [m/sec]
Distance difference [mm]
Delay time [msec] =
0.9 x Distance difference [ft]