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PCM3794 sample rates

Robert9862
Intellectual 310 points
Other Parts Discussed in Thread: PCM3794

I want to use a PCM3784 with a system clock of 12.288MHz.

Is it possible to use an arbirary sample rate (28817Hz or 43945Hz) if the codec is in slave mode?

Or are the allowed sample rates restricted to the ones in table 12 in the datasheet (also in slave mode)?

Robert

  • 0
    TI__Guru 55826 points

    It isn't possible to use an arbitrary sample rate if the codec is in slave mode.

    The restrictions in table 12 still apply.

    An alternative that supports your sample rates would be the AIC3204 - however this one is lacking the class-D power amp. Do you need the class-D power amp?

  • 0 in reply to Dominik Hartl11
    Intellectual 310 points

    I don't need the power amp, but I want to use the DSK_AUDIO4 board which has two PCM3794 codecs an an 12.288MHz oscillator on it:

    http://www.educationaldsp.com/stockproduct_dsk_audio4.htm

    But how do I determine the relation between system clock and sampling rate in slave mode? In my understanding, the NPR and MSR bits apply only in master mode.

    What if I derive (by the sample rate generator of the McBSP) a sampling rate of 27429 = 12.288M / 488 from the master clock? The only restriction for the system clock I can find in the datasheet is on page 21 (BCK and LRCK should be synchronized with audio system clock. Ideally, it is recommended that they be derived from it).

    Or would it be possible to generate an arbitrary system clock by timer1 of the dsp (DSK_AUDIO4 provides this possibility by switching J10)? But here is again the question: do I need 256*fs or 384*fs or something else as system clock?

  • 0 in reply to Robert9862
    TI__Guru 55826 points

    Even in slave mode, the NPR & MSR bits will define the sample rate. In Master Mode, the codec will put out the bit clock and LR clock. In Slave Mode, those still must be synchronized with the system clock.

    You can achieve your sampling rates by applying a custom system clock. For example, fs=27429, NPR=0, MSR=010 => SCK = 256 * fs = 7021824 [Hz].