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PCM5252: PCM5252 DAC IC Volume Control, and miniDSP Programming Capabilities

shadders
Expert 1065 points
Part Number: PCM5252
Other Parts Discussed in Thread: PCM5242, PUREPATHSTUDIO, PCM5142, SRC4392

Hi,

I am examining the use of PurePath and the TI PCM5252 DAC for use in a 3 way active speaker project.

The PurePath technical documentation is quite lacking in what is available, so I have requested to access the software to see how it functions and the capability.

In the interim, I am examining the use of the PCM525 as the DAC to be used for each loudspeaker driver path, and as a volume control.

Since the speaker system is an active 3 way design, then I will require 3 Stereo DAC IC’s. Each DAC IC will implement either the low frequency, midrange frequency, or high frequency signals.

Until I obtain the software for Purepath, I am unable to determine if the miniDSP on the DAC can implement the required filter – a Linkwitz-Riley 4th order low pass, or bandpass, or high pass. In addition, I may wish to implement some form of equalisation in the bass path.

The questions I have are as follows :

  1. For the PCM5252, page 0, register 61 and register 62 are the digital volume control registers. Are these registers directly writeable and directly readable ?

  2. Can the PCM5252 remember the volume setting after a power down ?

  3. Can one ensure that upon power up, that the DAC’s IC’s are muted and that a microcontroller can then apply the last used volume setting ?

  4. Can the PCM5252 miniDSP programming be used to implement a low pass filter, band pass filter, high pass filter, all 4th or 8th order Linwitz-Riley ??

  5. Can the PCM5252 miniDSP implement a delay to compensate for the speaker time delay for the specific drivers physical offsets related to the driver sound focal point transmission ?

  6. What are the limits of the delay possible (if possible) in the miniDSP, if the output sample rate of the PCM5252 is 192kHz or 176.4kHz ???

  7. If the output sample rate is either 176.4kHz or 192kHz, can the delay be selectable, such that delay1 is used for 176.4kHz and delay2 us used for 192kHz ???

If the PCM5252 can implement the filters, delays, and volume control, then this solution is much more efficient that using a DSP Core and DAC IC’s.

Thanks and regards,

Richard.

  • 0
    TI__Guru 53773 points

    Hi Richard,

    A few comments: The PCM5242 and PCM5252 are nearly identical devices, with the PCM5252 having some slightly modified DSP ROM components to support it 'SmartAmp' functionality.  These features are very specific for speaker characterization applications, so in general the PCM5242 should be used a more versatile device.  In addition, the SmartAmp features are not publicly supported by the PurePath software ecosystem, and we do not sell an EVM for the PCM5252.  For these reasons you should be using the PCM5242.  

    For the PCM5242 we support the DSP configuration via some pre-defined hybrid flows.  These flows can be experimented with using PurePath Console 2.

    www.ti.com/.../slau577a.pdf

    In regard to your questions

    1. The volume registers are accessible at all times and are read/write capable.

    2. The PCM5242 does not offer any user accessible ROM memory, all configuration and DSP registers will be lost after a power-cycle.

    3. At POR the XSMT pin can be asserted to keep the device muted.  The DSP can then put the device in standby as the register are re-written.  

    4. The DSP can implement many biquad filter typologies, but they are limited based on the sample rate.  For example, at "single-rate" sample rates (8-48kHz) the DSP can execute 1024 instructions.  At "quad-rate" 179.4kHz - 192kHz, the device can only execute 256 instructions.  I believe at quad rate you can use 1-biquad effectively with Hybrid Flow 5.  A custom flow might be able to support more, though in general I do not recommend custom flows as PurePathStudio is not well documented for the PCM5242 and it was never the primary development model.

    5. Delays can be implemented depending on the sample rate.  I believe Hybrid Flow 3 supports delays up to 16 samples at the single rate configuration.

    6. The high sample rate significantly limits the DSP's instruction set.  HybridFlow 5 supports the quad-rate inputs.

    7. The DSP should be configured based on the sample rate.  The DSP cannot modify the flow based on the input rate, but rather the host MCU should update the coefficients based on the changed input sample rate.

    Overall, this can probably be supported by the PCM5242 (or the PCM5142, which has custom flow support with the PurePath Studio tool).  You will need to balance the features you desire to fit with your instruction budget, as you are limited at the quad-rate.

    Have you been approved for PurePath Console/Studio yet?

    Thanks,

    Paul  

  • 0 in reply to Paul_Frost
    Expert 1065 points
    Hi Paul,
    Thanks for the reply and the answers.

    I have not yet been approved for PurePath, as i only applied today. I have previously read the PCM5252 datasheet - but did not fully appreciate the miniDSP capability.

    I will focus on the PCM5242 - thanks for the guidance here. Once i obtain access to PurePath, i can attempt the design required.

    The sample rate and 16 samples delay is sufficient for me to implement the longest delay required for standard CD sample rate.

    If the filter and delay cannot be accommodated in the DAC, then i can select the most appropriate design, and implement the other function elsewhere - once i understand PurePath etc.

    For the MCU modifying the coefficients, a quick look at the application note, i can see that the .cfg file will provide the relevant coefficients depending on the flow required. This means that i do not need to run at the quad rate (one size fits all approach) - i was going to implement the SRC4392 to convert all incoming audio data to 192kHz.

    Again, thanks for the answers - has provided a very good overview on what approach to take.

    Regards,
    Richard.