Subject: Re: [linux-audio-dev] protux, stereo and interleaving
From: Iain Sandoe (iain_AT_sandoe.co.uk)
Date: Fri Feb 09 2001 - 14:36:21 EET
Hi Steve!
On Fri, Feb 09, 2001, Steve Harris wrote:
> On Fri, Feb 09, 2001 at 12:19:49PM +0100, David Olofson wrote:
>> On Friday 09 February 2001 11:57, Iain Sandoe wrote:
>> > > - the time to [de]interleave data is a knats-p in a
>> > > millpond compared to doing 600+ FFTs in real-time...
>> >
>> > Agreed.... and one can apply this argument to many facets of the
>> > process... unfortunately you then end up with 10**N gnats... which
>> > is one hell of a lot of p.
>>
>> Yep, another good argument. That's another reason why I'm not just
>> throwing the pitch in.
>>
>> BTW, this pitch value is more easy to use than it may seem. From the
>> Host perspective, it's just a matter of telling a Plugin how many
>> physical channels a buffer has when connecting one of the Plugin's
>> Buffer Slots to it. (Pitch is effectively # of channels * sample
>> frame size in any normal buffer.) Use the channel number to index the
>> buffer pointer when calculating the pointer to pass to the Plugin.
>
> Maybe I'm missing someting, but most complex plugins require filters
> which require deinterleaving the data anyway.
>
> Also, I think you are better off (if you can) running small loops
> over each channel in series, rather than a more complicated loop over
> serveral channels at once - less cache polution.
That depends on how you code multi-channel functionality.
If you know, a priori, that you are dealing with a "stereo" process and have
a simd machine it might pay to feed the samples in cross-wise blocks -
keeping all execution units busy with the same instruction.
This (for some of my applications) might become more acute (I have in mind
scientific applications where I might have, say, 8 channels all considered
and processed as a group).
not, maybe mainstream requirement - but a couple of euros for the pot.
Iain.
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