[linux-audio-user] Sending and recieving data between computers using JACK

[Edward Barrow]

On Wednesday 18 August 2004 15:20, Joe Hartley wrote:
> I live in a house with 4 distinct areas, with network connected music
> systems in each area.  When I have a party, I'd love to have each of
> these machines tie into a stream from my audio server so that they're
> in sync - that is, if I can hear 2 different systems at the same time,
> I want them to be at the same place in the stream, not a second or two
> off from each other.

I don't think the problem you describe is anywhere near as simple as just 
getting the streams into sync - although it depends on the size, and to some 
extent the shape and construction of the house. You have to consider how the 
sound reaches your ears from each set of speakers, and this is far from 
straightforward since sound waves of different frequencies are likely to 
travel by different routes.  Sound reflection, diffraction, absorbtion and 
interference all affect different wavelengths differently.  The simplest way 
to get the sound in 2 zones in sync is to transmit the analogue audio between 
the two; if you do that, and stand in the middle, you'll get far from perfect 
sound in the middle spot, because of these effects which tend to outweigh the 
loss of quality through attenuation and interference in the analogue 
electrical stage in the wires. Your proposal (synchronised streaming) 
effectively resolves the analogue attenuation/interference issues by using 
digital transmission in the wires, but ignores all the acoustic effects.

However, there may be another application.... 
In bars and other public places, the current fashionable trend for hard 
[white] walls and ceilings which reflect shorter-wavelength sounds well 
exacerbates the conflict between music and conversation, so that it becomes 
impossible to hear either above the din of both. Bass notes are much less 
affected and travel well at ground level through a mass of people. I think it 
should be possible, with a combination of softer sound-absorbing surfaces and 
smaller, localised mid-range and treble speakers, to create in a busy place 
like a bar an acoustic environment where the volume of conversation and music 
is as balanced as it is in your living-room with say half-a-dozen guests. 
This might require some variable multiple millisecond delays to be introduced  
to the signal to the localised speakers so that the treble is in sync with 
the bass...  This is however, nothing more than a thought experiment brought 
on by the frustration of spending too much time in such noisy environments, 
so I'd be glad of comments!

Edward Barrow