Re: Basic question
Re: Basic question
- Subject: Re: Basic question
- From: Matthew Johnson <email@hidden>
- Date: Wed, 27 Mar 2002 22:38:04 +1100
The information I have retrieved is:
input mSampleRate = 44100
input mFormatFlags = 0000000B
input mBytesPerPacket = 8
input mFramesPerPacket = 1
input mChannelsPerFrame = 2
input mBytesPerFrame = 8
input mBitsPerChannel = 32
What I don't understand is what each float value actually is. Can I
determine from each value ( which I am assuming is a sample ) the Amplitude
in Db's and the frequency in Hz.
I.e if I record some audio I seem to get floats within the range of -0.4 to
0.4 (I don't know what the units are) As far as I can deduce each value must
represent a Amplitude and a Frequency.
I could be completely wrong. I am a total newbie to this.
Matt
On 27/3/02 10:02 PM, "Laurent Cerveau" <email@hidden> wrote:
>
On Wednesday, March 27, 2002, at 11:35 AM, Matthew Johnson wrote:
>
>
> Very simple question I suspect but I can't find the answer anywhere.
>
> Following is my IOProc for recording from my microphone. It works well.
>
> The
>
> only thing I am wondering is what is the actual data in the array of
>
> floats?
>
> What is its scale?. How do I retrieve the Amplitude and frequency from
>
> the
>
> data?
>
>
>
>
What are you trying to achieve?
>
>
The data will be ... the microphone input data converted from native
>
device format (16 bits, 8bits...) to floats . You can ask for the
>
properties of the device through CoreAudio calls
>
(AudioDeviceGetPropertyInfo, AudioDeviceGetProperty), or for the stream
>
info, but this will give you the settings of the hardware device not
>
about the data themselves.
>
>
If you want to do further analysis of the data you will have to deal
>
yourself with FFTs and other DSP niceties (in this case you may want to
>
have a look at the vecLib framework)
>
>
Laurent
>
>
Laurent Cerveau
>
Applications Division
>
Apple Computer Inc.
>
email@hiddenrent
>
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