TAS2770: 96kHz frame rate behavior

Hi Eric,

Welcome to e2e.

I'll take a look into this, we haven't been notified of something similar before.

Just to verify, are you using AUTO_RATE? or are you manually setting the sample rate on register 0x0A?
SBCLK/FS ratio is the same for both sampling rates, correct?

Additionally, can you share your configuration script? Did you obtained it from PurePath Console 3?

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

I was able to reproduce this problem using Purepath3 and the EVM this weekend.  Register dump is attached (note: this is done on left channl, I am not using right channel on evm right now).

It appears the problem is isolated to when I am using L+R/2 mixing in the codec.  When in this mode, with SBCLK/FS ratio of 64, the DVC is inoperative and the ouput is louder in 96kHz vs 48kHz.  The "louder" comparison was done with the DVC set to 0dB for both 96 and 48.  I have tried it with both auto clock detection and with manual programming of clocks and the results are the same.  Visual comparison of oscilloscope captures for both our product and the EVM driven by purepath are the same. 

We can modify our upper layers of SW to do the L+R/2 mixing, so operating TAS in one of the mono modes isn't a problem.  However I am reluctant to apply this change and assume all is well, concern being that there may be some other underlying problem that this is masking.  Feedback on the L+R/2 discovery would be appreciated.

PurepathDump.h

Hi Eric,

I'll test this out on my side as well and provide comments about it.
If a fix is needed to operate the device in 96kHz I'll inform as well.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

Hi Eric,

I tested TAS2770EVM on my side and found some interest things:

• Neither DVC_PCM or AMP_LEVEL work for 96kHz sample rate, the output is the same regardless of the value of these registers.
• DVC_PCM and AMP_LEVEL work correctly when using 48kHz or 192kHz
• As you pointed out, DVC_PCM and AMP_LEVEL work correctly using 96kHz and any slot select config but stereo down-mix

Based on this, I'll check with our team why this specific combination causes the volume control not to work properly, if there is a fix and timeline for its development.
Will give you an update on this by the end of the week.

The specific case is (all other cases work correctly):

• 96kHz sample rate and stereo down-mix

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

Thanks Ivan.  I was able to do the down-mix in the host SoC's i2s block and configure the tas2770 for mono using left channel slot.

In this configuration my tests indicate that everything is working properly with respect to the datasheet. This will be an acceptable solution for our product.