Re: Out-of-range samples
Re: Out-of-range samples
- Subject: Re: Out-of-range samples
- From: "B.J. Buchalter" <email@hidden>
- Date: Mon, 30 Jan 2006 11:47:08 -0500
- Thread-topic: Out-of-range samples
on 1/30/06 10:01 AM, Erik Rose at email@hidden wrote:
>> It is odd that the driver for the built-in mic is producing such
>> high sample values. The driver must have a built-in gain control
>> that is set very high. You should be able to access the gain
>> control in AMS.
>
> Unless I have a profoundly mistaken view of the universe, CoreAudio
> should stay within its amplitude limits no matter how high the gain
> is cranked up. If the gain is too high, it should, at worst, clip,
> yielding ones and negative ones. I take it you haven't encountered
> these out-of-range values?
For some devices/drivers the gain control exported to CoreAudio (and AMS) is
a digital domain gain control in the driver (not an analog gain control
before the conversion step). AFAIK, there is no way to discover which type
it is with the current API (although I am sure Jeff will correct me if I am
wrong about that).
For the built-in audio (at least on current machines) the input gain is a
digital domain control that applies a floating point scalar to the converted
samples. As a result, the samples coming from the hardware are clipped to
+/- 1, but the samples coming from the driver will have a clipping point
that is scaled by the gain that you set (so if the gain is > 0dB, the
samples you receive from the driver can have a magnitude > +/-1).
Hope that clears up the issue.
Best regards,
B.J. Buchalter
Metric Halo
5 Donovan Drive
Hopewell Junction, NY 12533 USA
tel +1 845 223-6112
fax +1 603 250-2451
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