ADAU1372 anti-aliasing filter at 16 kHz sample rate


I am using a ADAU1372 codec at a sample frequency of 16 kHz and from measurements I found that a frequency of 8.1 kHz at the ADC input appears only 6 dB lower at 7.9 kHz at the ADC output (when compared to signals < 8 kHz) and that a signal of 7.9 kHz at the DAC input appears as two signals at the DAC output at 7.9 kHz and 8.1 kHz only 6 dB lower.

I would expect that an digital anti-aliasing filter was in place of at least - let's say 40 dB, but obviously that is not the case.

I am doing something wrong? Is there a setting to enable a digital anti-aliasing filter for a 16 kHz sample frequency?

If no, then does Analog Devices have a codec with similar requirements (sound quality, latency, power consumption) but with an anti-aliasing filter for a sample frequency of 16 kHz (possible alternatives: 24 kHz or 32 kHz)?

I can work around the problem by using the sample frequency of 48 kHz (or higher), which has a good anti-aliasing filter according to the specifications, and implementing my own sample rate converter with digital filter, but I prefer to have this done by the codec.

Kind regards,

Ad van de Voort

Videtur BV