[Liverpool] Silent PCs

[Bob Ham]

On Fri, 2011-06-17 at 21:13 +0100, Sebastian Arcus wrote:
> On 17/06/11 20:59, Andrew Bates wrote:
> > that would introduce too much latency for audio production work ;)

> On the other hand, I remember managing to process sound with a lowly 486 
> DX4. I was under the impression that compared to video work, sound 
> doesn't require that much CPU.

Latency is the time it takes for a signal to traverse a system.  This is
usually irrespective of CPU power.

Say you have a music keyboard connected to a computer running a software
synthesiser, and the computer is again connected to some speakers.  The
latency is the amount of time it takes for sound to reach your ears
after you've hit a key on the keyboard.  This will be governed by, for
example:

1. Whether the kernel can suspend disk access or other activity in order
   to service MIDI port interrupts
2. The size of the output buffer in the sound card
3. The length of the speaker cable
4. The distance of the listener from the speakers


In a real-time system (ie, a proper audio system like JACK¹), the
software synthesiser will execute within chunks of time based on the
size of the sound card's output buffer.  The amount of time it has in
each chunk is the latency.

During any particular chunk, the synthesiser may take up 10% of a 486 or
95% of a Sandy Bridge to generate it's sound, that makes no difference.
The amount of *time* is always bounded and that time is the latency.

Hope that helps clarify :-)


¹ http://www.jackaudio.org/

-- 
Bob Ham <rah at bash.sh>

for (;;) { ++pancakes; }
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