On 22/09/2013 12:51, Andy Furniss wrote:
Hi
I do not have a 7.1 sound system so can't actually test this, also as
may become apparent I don't know much about sound :-)
I would be grateful if someone could correct/confirm the following.
If I were to mix down a digital 7ch to mono I have to reduce by 1/7
amplitude to prevent clipping, so one channel will be -16.9dBfs.
This assumes that all 7 channels are driven with the same maximum level,
in phase, and that this would get past the mastering stage,,
I'm sure they bear in mind the possibility of stereo, or mono mixdown.
If I play the track over one speaker the volume difference between one
and all channels will be 16.9dB.
If I were to measure the volume at listening position (assuming
anechoic and equal speaker distance) with a real 7 speaker setup then
the volume difference, because the speakers are not close, would add
up using power not amplitude so the difference heard/measured between
1 and 7 at full power would only be 8.45dB, so there is quite a large
dynamic range discrepency?
You would add powers if the 7 channels had random relative phase (which
is less likely with "anechoic and equal speaker distance"
The real reason for this question is more to do with simulation than
real life, so perhaps that will make a difference - if the speakers
are infinitely far producing planewaves and a soundfield is at
listening position would that change anything for what levels the
virtual omni would "hear".
TIA
Andy.
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