linuxaudio.org

On Tue, Oct 05, 2010 at 02:50:10PM +0200, David Olofson wrote:
> Not only that. As long as the "fragment" initialization overhead can be kept

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> low, smaller fragments (within reasonable limits) can also improve throughput

> as a result of smaller memory footprint.

'Fragment initialisation' should be little more than

ensuring you have the right pointers into the in/out

buffers.
> Depending on the design, a synthesizer with a large number of voices playing

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> can have a rather large memory footprint (intermediate buffers etc), which can

> be significantly reduced by doing the processing in smaller fragments.

> Obviously, this depends a lot on the design and what hardware you're running

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> on, but you can be pretty certain that no modern CPU likes the occasional

> short bursts of accesses scattered over a large memory area - especially not

> when other application code keeps pushing your synth code and data out of the

> cache between the audio callbacks.

Very true. The 'bigger' the app (voices for a synth, channels for

a mixer or daw) the more this will impact the performance. Designing

the audio code for a fairly small basic period size will pay off.

As will some simple optimisations of buffer use.
There are other possible issues, such as using FFT operations.

Calling a large FFT every N frames may have little impact on

the average load, but it could have a big one on the worst case

in a period, and in the end that's what counts.
Zyn/Yoshimi uses FFTs for some of its algorithms IIRC. Getting

the note-on timing more accurate could help to distribute those

FFT calls more evenly over Jack periods, if the input is 'human'.

Big chords generated by a sequencer or algorithmically will still

start at the same period, maybe they should be 'dispersed'...
Ciao,
--

FA
There are three of them, and Alleline.
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