Re: kAudioUnitID_BandPassFilter
Re: kAudioUnitID_BandPassFilter
- Subject: Re: kAudioUnitID_BandPassFilter
- From: Lieven Dekeyser <email@hidden>
- Date: Sat, 12 Jan 2002 00:05:44 +0100 (CET)
>
> the reason I'd like to know is I would like to implement something like
>
> the equalizer in iTunes, so I'd take some Band Pass filters each for a
>
> different frequency interval, pass the audio data through them, and then
>
> mixing the output back together adjusting the gain. Is this the right
>
> way
>
> to do it, or are you all laughing at me right now? :-)
>
>
This will work--sort of. The problem is that all audio filters cause
>
phase shift, to differing degrees depending on their design and the
>
parameters they're using. Where your filters overlap, you will be mixing
>
together sound which has been phase-shifted by different amounts, and
>
this will probably sound pretty terrible. You can get around this by
>
being careful about the particular filter design you use; unfortunately
>
we have no details about how exactly the filters in the Apple audio
>
units work, as far as I know.
can anyone at apple tell us more about it?
I guess I'll drop the equalizer plan if the phaze shifting differs too
much for different frequency intervals, because I don't have the time nor
the courage to start digging deep into digital signal processing. I was
really glad to see all those effects CoreAudio is capable of without /me
becoming a dsp professional :-)
Maybe an idea for those dsp professionals at apple: an equalizer
AudioUnit... wouldn't that be cool?
My other option is bass & treble gain in stead of a complete equalizer. Is
this hard to implement using the AudioUnits?
thanks,
--Lieven