Re: low-pass filter on the iphone (William Stewart)
Re: low-pass filter on the iphone (William Stewart)
- Subject: Re: low-pass filter on the iphone (William Stewart)
- From: William Stewart <email@hidden>
- Date: Tue, 9 Dec 2008 12:50:44 -0800
On Dec 9, 2008, at 6:55 AM, Roni Music wrote:
audio units do NOT deal with compressed audio - they never have, nor
do we have any plans to make them.
if you want to deal with compressed audio, then you need to use the
audio converter or audio queue APIs
But as far as I know, on the iPhone audio converters doesn't handle
compressed audio (on Mac OS X it works 100%)
They handle some - any codecs that don't need hardware assist (so IMA,
uLaw, aLaw, ilbc) will work just fine.
and to be able to perform some DSP on the decompressed audio by
using audio queue APIs,
one should use AudioQueueSetOfflineRenderFormat /
AudioQueueOfflineRender.
In one of you earlier answers you said:
"AudioQueueRenderOffline is meant to enable this, but we are still
looking at some issues here -
I don't have any update to this at this stage"
We're preparing a document that describes how to use this
Can you confirm that currently AudioQueueRenderOffline doesn't work
as intended?
It would be very good to get a confirmation about this, then we can
stop trying to solve a problem that
currently has no solution.
Thanks,
Rolf Nilsson / Roni Music
So, I'm not sure what "confirmation" you are wanting.
Bill
On Dec 6, 2008, at 12:16 PM, Daniel Birns wrote:
2) Currently I'm using AudioQueue and doing my processing in the
player callback. My current processing is very simple -- I look
for
peaks, and shift as necessary to amplify the sound. I realize
that
audiounits is the preferred method for this, but since I don't
mind
some delay in the start of the playback, I wonder if I should
simply
continue like this, since it's simpler.
sure - there's no reason not to be doing what you are doing, where
you
are doing it
But doesn't this mean it will only work with PCM files?
At this point
(I assume this is just before callingAudioQueueEnqueueBuffer() )
mp3 files and other compressed formats are not yet decoded into PCM
format.
I'm asking this since I'm struggling with getting the
AudioQueueOfflineRender() function to work
to be able to perform some DSP processing to the audio before
sending it out
to the audio out device.
The way I use AudioQueueOfflineRender() it produces silence only.
Would appreciate if somebody could explain how to use
AudioQueueOfflineRender() in a correct way.
The available documentation is very sparse and no sample code
Right -- I presume this implies pcm. I will need compressed format
eventually, and I've assumed that I'll have to go to AudioUnits to
do my processing in that event... But a confirmation would be
appreciated...
--Daniel
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