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TLV320AIC3254: PurePath Studio GDE and miniDSP Custom Decimation Filters

Miguel Carvalho
Prodigy 170 points
Part Number: TLV320AIC3254
Good Day
Please see previous interaction with TI support:
Question:
"Using the signal processing blocks on the AIC3204 and the provided ADC filter C there seems to be a bandwidth limitation of 20kHz with 192kHz operation.
Could an AOSR of 32 be used with ADC Decimation filters other than Type C. We would like to be able to sample at 192kHZ using Type A or Type B. Is this advisable?"
TI Support Reply:
"192 kHz operation for the AIC3204’s ADC is specified for Filter C only, which has a bandwidth 20 kHz.
Filter B can be used with an OSR=32 at 192 kHz but it will result in a gain error of -24dB (see picture in
attachment). The ADC has a digital PGA gain that can then be adjusted to +20dB, but will still have
-4dB gain error.
The AIC3254 could be used instead of the AIC3204 to create a custom decimation filters for 192 kHz
sampling rate by bypassing the input signal to the miniDSP instead of the processing blocks’
decimation filters.
"
Subsequently to this we are now attempting to use the AIC3254 miniDSP and PurePath to produce these "Custom Decimation Filters".
At first glance the decimation blocks in PurePath use the same filters in the signal processing blocks (Filter A, B and C). In addition the the filter blocks, for example the FIR filter only allow the number of taps and the taps to be specified. There seems to be no way to specify a decimation factor or any alternative to decimation with a custom filter.
Is there something that we are missing, any advice would be highly appreciated.
Kind Regards
Miguel Carvalho
  • 0
    TI__Guru 57800 points

    HI, Miguel,

    Welcome to E2E, thanks for your interest in our products!

    Regarding your question, there is a post in the forum where the procedure to implement this application is explained, so you can use it as reference.Please take a look to this post. 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 170 points
    Hi Diego

    Thank you very much for your response.

    I am aware of the method you refer to. It is not exactly what we would like due to the digital gain applied which will amplify the noise and thus decrease performance for our application (Modem Waveform).

    We ideally would like to create a "Custom Decimation Filter" for instance if we could use the FIR Filter block and some how decimate in the process. Is this in any way possible? So bypass the use of Filter A,B or C completely.

    Or was the previous statement by TI Support ("The AIC3254 could be used instead of the AIC3204 to create a custom decimation filters for 192 kHz sampling rate by bypassing the input signal to the miniDSP instead of the processing blocks’ decimation filters.") slightly misleading. As we interpreted it as a separate method to the method your reply points to.

    Kind Regards
    Miguel Carvalho
  • 0 in reply to Miguel Carvalho
    TI__Guru 57800 points

    Hi, Miguel,

    Unfortunately the creation of custom blocks, like a separate decimation filter, is not supported in PurePath Studio. The method you describe is actually the same provided in the post I referenced before, where the filters within the miniDSP are used.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 170 points

    Hi Diego,

    Thank you for your reply.

    That is unfortunate. I was hoping to achieve a more optimal decimation filter, but thank you for your help.

    Best Regards

    Miguel Carvalho

  • 0 in reply to Diego Melendez
    Prodigy 170 points

    Hi Diego,

    Regarding the post you referred to:

    I am battling to understand the Decimation step in the process flow.  The setup involves setting up a AOSR =  32, therefore I would assume there is a decimation filter with a factor of 32 somewhere to achieve the 192kHz Sampling Rate ? What am I missing here? Is there any decimation happening before the miniDSP?

    Best Regards

    Miguel Carvalho