linuxaudio.org

On Tue, 5 Oct 2010 22:00:11 +0200

fons@kokkinizita.net wrote:
> On Tue, Oct 05, 2010 at 02:50:10PM +0200, David Olofson wrote:

quoted text
>

> > Not only that. As long as the "fragment" initialization overhead can be kept

> > 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

> > 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

> > 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,

I'm all in favour of a bit of dispersal.
When I started out with a Yamaha SY22 and Acorn Archimedes it was all

too easy to stuff too much down the pipe at once. However, doing some

experimenting, I was surprised at how much you could delay or advance

Note-On events undetectably although it depended to some extent on the

ADSR envelope.
I don't need to do that any more, but old habits die hard, so if I'm

copy-pasting tracks I tend to be deliberately a bit sloppy.
I'm also a bit puzzled by people complaining about jitter. I don't have

any exceptional kit, but in reality I can't say I've ever noticed it.

Latency yes, but that's easily corrected with a bit of post record

nudging.
--

Will J Godfrey

http://www.musically.me.uk

Say you have a poem and I have a tune.

Exchange them and we can both have a poem, a tune, and a song.

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