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Re: Sample Rate Converter Questions
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Re: Sample Rate Converter Questions


  • Subject: Re: Sample Rate Converter Questions
  • From: James McCartney <email@hidden>
  • Date: Wed, 25 Jun 2014 16:53:17 -0700

On Dec 30, 2011, at 10:07 PM, Tim Murison <email@hidden> wrote:

> Hi,
>
> I'm looking to use the built-in Core Audio sample rate converter on OS X such that I get the highest quality output. To that end, I'm using the Pre prime method,

Pre priming mode does not change the quality. Pre is for when you are sample rate converting audio from the mid point of a stream and you want to prime it with with sample before time zero. This will result in an “attack" that preserves the preceeding content. Normally you want the first sample of output to correspond to the first sample of input and for this you should use the Normal mode.


> however in the callback the PrimeInfo struct always has 0 for leading and trailing frames. I do notice that the first call to the callback requests more frames than subsequent calls, but it isn't clear to me when to provide leading or trailing frames. The only time leading and trailing frames are non-zero, is if I set None for the prime method.

You should also see it for Pre.

>
> Am I doing something wrong?
>
> Also, I am trying to understand what the initial phase setting means. Does this control the amount of pre-ring vs. post-ring? If not, what kind of audible effect would this option have?

Initial phase is for when you have a need to have sub-sample accuracy to specify the start of the wave. It has nothing to do with pre-ring.

>
> Thanks!
>
>
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James McCartney
Apple CoreAudio
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