Re: Convolution with large filters?
Re: Convolution with large filters?
- Subject: Re: Convolution with large filters?
- From: Nikolai Collinsky <email@hidden>
- Date: Sat, 11 Feb 2012 20:54:18 +0000
Hi Michael,
Partitioned convolution is your friend here for longer impulse responses. You might have to write some convolution code yourself going via FFT calls.
For the minimal delay version of this, see:
William G. Gardner. Efficient convolution without input-output delay. Journal of the Audio Engineering Society, 43(3):127–136,
1995.
There are open source (GNU GPL 3) C++ code examples amongst SuperCollider UGens (my partitioned convolution implementation PartConv, and Stefan Kersten's VEP with the minimal delay trick) that might give some guidance, though couldn't be directly used as source, but I'm sure you could write your own.
Thanks for the indirect iOS RemoteIO hints a few years back, via Aran Mulholland's tutorial posts and links to your code...
best,
Nick
On 11 Feb 2012, at 19:38, Michael Tyson wrote:
> Hello!
>
> I'm putting together a convolution audio filter using Accelerate's vDSP_conv, and I'm wondering about what practical filter limits I should be expecting?
>
> I'd like to use it with arbitrary impulse responses (for example, I'm testing with a lovely, echoey hall impulse response, which is about 2 seconds in length).
>
> I've noticed that filters with more than about 16k frames (0.4s) seem to overwhelm the system, causing jittering.
>
> < 0.4s filters are perfectly adequate for things like lowpass filtering, but for nice resonance/natural decay effects, it's way too short.
>
> So, I'm wondering - is there a more appropriate way to use these reasonably long impulse response filters? How does professional sound engineering software handle this kind of thing?
>
> Am I dreaming, and do I just need to limit filters to 16k?
>
> Many thanks,
> Michael
>
>
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