Re: low-pass filter question
Re: low-pass filter question
- Subject: Re: low-pass filter question
- From: William Stewart <email@hidden>
- Date: Wed, 11 Jan 2006 12:20:51 -0800
There are also different quality settings for the resampler - you
should set these to maximum. This does make a substantial difference.
I don't know what quality settings were in use in the tests quoted
below.
Bill
On 11/01/2006, at 8:11 AM, Antoine Missout wrote:
You probably want to take a look at this.
http://www.audioease.com/Pages/BarbaBatch4/Barba4SRCTest.html
Antoine
On 11-Jan-06, at 2:30 AM, Rustam Muginov wrote:
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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