Re: low-pass filter question
Re: low-pass filter question
- Subject: Re: low-pass filter question
- From: Rustam Muginov <email@hidden>
- Date: Wed, 11 Jan 2006 10:30:00 +0300
Bill, does it use the same AULowPass? Or other filter?
What are the parameters for the filter? What are the characteristics?
I had also found what resampler build-in into OS X does not have
acceptable for our tasks characteristics.
Thank you.
--
Sincerely,
Rustam Muginov
On Jan 11, 2006, at 4:41 AM, William Stewart wrote:
The resampler does all of this filtering for you before it resamples.
You don't need to do anything else
Bill
On 10/01/2006, at 10:43 AM, Dan Morgan wrote:
I am working on an application where audio data is being sampled at
48kHz. Because I am only interested in frequencies below around
6-8kHz (and am interested in data reduction), I apply the Apple
low-pass filter audio unit with cutoff frequency 7kHz (to prevent
aliasing of frequencies above 8kHz) and then downsample to 16kHz
using a format converter. This should work fine if the low-pass
filter response is sharp.
The problem is that the Apple low-pass filter has a response that is
anything but sharp. I set up a little test program that injected
sine waves of different frequencies and found that frequencies of
half the cutoff were being significantly attenuated and frequencies
of double the cutoff had a significant fraction passed. This is not
acceptable behavior for the intended application.
A couple questions: (1) Does the Apple format conversion have any
internal anti-aliasing low-pass filtering that it does when it
downsamples (hence making other low-pass filtering unnecessary)? (2)
If not, do you have any suggestions for how to proceed, e.g. any
other low-pass filters to consider?
Thanks.
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