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: "Roni Music" <email@hidden>
- Date: Sat, 6 Dec 2008 13:41:11 +0100
On Dec 4, 2008, at 10:23 AM, Daniel Birns wrote:
I'm a newbie to dsp. I need to do some simple dsp to improve voice
recording on the iphone. I currently have some simple processing
working reasonably well, but I'd really like to improve the quality
of the result.
Questions:
1) The mac provides many audiounits that I could use. Is there any
dsp provided for iPhone developers, or must I code this myself?
we haven't provided many filters, etc for iphone at this point. what
would you like? (Please file a bug report - best way to get these
requests to us - http://bugreporter.apple.com)
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
Thanks,
Rolf Nilsson
3) What algorithms are recommended for voice, particularly recording
lecturers at some distance from the mic? Compression, low-pass
filter, amplification?
4) Assuming I have to write my own, can anyone direct me to sample
code that implements something that would work well on the iphone
probably the musicdsp list is a good forum for that
Bill
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