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General question
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General question


  • Subject: General question
  • From: Daniel Birns <email@hidden>
  • Date: Tue, 4 Nov 2008 17:10:18 -0800

Two questions:

My application will do automatically change the (HAL/preamp) input volume, and adjust for this later in the playback process. I could use some advice about how best to accomplish this.

To take a simple example: During recording my input AudioUnit determines that the volume needs to be higher. So I change the HAL input volume (not the recorder trim value) up by, say 6 db at time t. (I know most devices don't support this yet -- but the built-in mic does, and I'm working with manufacturers on getting their support.) Later, during playback, from time 0 to time t, I will add automatically add 6 db gain to the audio. I need only record the time (t) and the delta in volume (+6db) during the record process, and I need to get this information back later during playback or processing. Not a lot of data.

Questions:
1) Where can I store this volume adjustment (time/db) information? In track automation? in some data chunk in the wav file? In midi somehow?
2) Can an AudioUnit access HAL objects? For example, the audio unit usually has an opaque input source. Can I discover what that source is and operate on it?
3) Does apple provide SDKs for GarageBand and/or Logic so I can provide (non AU) plug-ins, if my product needs it for ease-of-use?


My eternal gratitude to the soul who is able to set me on the right track :-)

--Daniel
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