Using Sample Rate Converter (SRC) for low bit depth and low sample rate audio

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andy.heidt
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Joined: 2017-02-27 16:29
Using Sample Rate Converter (SRC) for low bit depth and low sample rate audio

Hello,
I would like to output a PDM stream from a low fidelity audio stream, but it's not clear whether the SRC and PDM peripherals support this. Here are my application details:

Audio file details:
- Stored in external flash
- Mono
- Bit depth: 8 bits
- Sample rate: 16 kHz

PDM output requirements:
- Either (a) 128x oversampled PDM at 2.048 MHz PDM clock or (b) 256x oversampled PDM at 4.096 MHz PDM clock
- Stereo output. One channel should be the mono audio file, and one channel can be any value (it is ignored by the next device in the audio chain).

In the SRC section of the datasheet, it lists the supported conversion as "SRC_IN (24 bits) to PDM_OUT (1 bit)". Additionally, it lists the SRC_IN sample rate as ranging from 62.5 kHz to 16 MHz.

Can the SRC and PDM peripherals support my input and output requirements? Can the SRC input handle bit depths down to 8 bits and a sample rate down to 16 kHz?

Thank you for the help,
-Andy

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MT_dialog
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Last seen: 1 year 7 months ago
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Joined: 2015-06-08 11:34
Hi andy.heidt,

Hi andy.heidt,

Yes, I trust that you can, the SCR will obtain the data by 24bit at a time so you will have add zero padding to your 8bit samples and provide each sample to the SRC, regarding the sample rate i ve checked with the designers, it seems that there is a mistake in the datasheet and the "SRC_IN, SRC_OUT Sample rates 62.5kHz to 16MHz" should be changed to "8kHz to 192kHz".

Thanks MT_dialog