PCM4202: seeing poor THD results

Hello,

This is a question from my customer, can you comment?  Please let me know if more info is needed.

Thanks.

From Customer:

I'm using the PCM4202 (24-bit audio A/D converter) in a new design.

I'm running the PCM4202 in the following mode:

- Data format is 24-bit I2S

- Slave Mode

- Single Rate with Clock Auto-Detect

- Enable High Pass Filter

The problem I'm having is when I measure the THD (total harmonic distortion), the THD at 32 kHz and 48 kHz sampling is about -67 dB and the THD at 44.1 kHz sampling is -89 dB.

All measurements done with a 1 kHz test tone with an Audio Precision test instrument set for a 22 to 22 kHz flat filter.

I've done a lot of other testing which I won't go into but everything I've done suggests the crappy THD problem at 32 and 48 kHz sampling is related to the PCM4202 only and not to any external circuits.

When I substitute a PCM1804 in place of the PCM4202 (everything else being identical) the THD is around -85 dB for all sampling rates (32, 44.1, and 48 kHz).

Why is the THD for the PCM4202 so lousy for 32 and 48 kHz sampling and OK for 44.1 kHz sampling?