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TAS5755M: DRC algorithm equations

Andrew Pines
Prodigy 20 points
Part Number: TAS5755M

I'm using a TAS5755M in an application.  I have it mostly working as required (2.1, BD mode, biquads used as active crossovers and bass/treble shelf filters).  I'm trying to get DRC working but am finding a dearth of documentation and some of what's there seems incorrect.  I'm not a filter expert so I may be missing something.  Is there an application note on how the DRC works?  I see references to sloa148.pdf in other posts but the links in the forum are bad and I've been unable to find that document anywhere.

I don't want the numbers that are dumped out the of the GDE, I want to be able to calculate them.  For example, the GDE can calculate alpha for energy, attack, or decay from milliseconds but I don't see the equation anywhere for me to do it in my software.  Additionally, all of the units are unclear.

The data sheet (TAS5755M SLOS982C –AUGUST 2017–REVISED APRIL 2018) references "TAS570X GDE Software Setup development tool documentation (SLOC124)" in section 9.3.7 but that tool doesn't list TAS5755M in its configuration and it doesn't come with any documentation beyond the built-in help which is more about how to use the tool than how the part works.

The data sheet allocates only a single page to DRC, page 33, section 9.3.11.  The graph shows T but not K or O and the register addresses in the chart appear to be incorrect.  So, overall, that section is not particularly helpful.

I appreciate any guidance you can offer.

     -Andrew

  • 0
    TI__Genius 13280 points

    Hi Andrew

    It is difficult to provide the detail calculation formula of DRC.

    all we can provide is the tool and simple explanation of DRC structure in the datasheet.

    if you have any config problem, we can discuss by e2e.

    thanks.

    jesse

  • 0 in reply to Jesse Ji
    Prodigy 20 points

    Hi, Jesse,

    I can't agree with that assertion.  After significant digging I believe I've found part of my answer in an unrelated component's data sheet.  It appears that the energy, attack, and decay values are calculated as:
       a=1-e^(-1000/(fs*tc))
    and, of course:
       w=1-a
    where fs is the internal sampling rate (e.g., 48,000) and tc is the desired time constant in milliseconds.  So, if that's correct then that's three of the six registers understood.  I can't fathom why that simple statement would be excluded from the data sheet for the TAS5755M.

    So, I ask more directly:
         1) is the above statement true for energy (0x3a/0x3d), attack (0x3b/0x3e), and decay (0x3c/0x3f)?
         2) is SLOC124 (TAS570X GDE) the correct tool to be using for TAS5755M?  If not, which one is?  If so, which device should be selected since TAS5755M isn't an option?
         3) does an application note (sloa148.pdf or otherwise) exist which details how the DRC works?

    I'm finding this to be a fantastic component with wretched documentation which is truly disappointing.  I'm hoping you can point me to better documentation and that TI will do better with documentation overall in the future.

         -Andrew

  • 0 in reply to Andrew Pines
    TI__Intellectual 2600 points

    Hi Andrew 

    I will check with our team for more information and then reply you.

  • 0 in reply to Andrew Pines
    TI__Intellectual 2600 points

    Hi Andrew

    The tools of TAS5755 is TAS57X1 GUI TAS57x1_v2.1_Build_8 (Rev. A) , you can download at TAS5755EVM introduce web.

    you can configure by this GUI, and don't need to calculate detail.

     

    however, you can also reference the application note for how DRC works, www.ti.com/.../slaa894.pdf

  • 0 in reply to Feeney Xiao
    Prodigy 20 points

    In my application I need to be able to calculate the time constants plus T, K, and O so they can be adjusted on-the-fly.  The time constants are explained in SLAA894 as I noted in my second post, above.  However, T, K, and O are not well explained.  For the benefit of anyone who may stumble on this in the future, here are the equations I backed out from the GDE by testing several values and working out the method that the GDE is using to calculate T, K, and O:

       T = (x-24.0)/6.0206
    where x is the threshold in dB and T is the value to write to the register.

      K = -(x-1)/x
    where x is the compression ratio.

      O = ( 2 * 10 ^ (x/20) ) / 31
    where x is the offset.

    They're not particularly complex.  I'm at a loss as to why none of this is in the data sheet or the app notes.  I can't represent that these are exactly correct since I couldn't find documentation about them anywhere but maybe this will save someone some time if they need to calculate these values on their own.

         -Andrew

  • 0 in reply to Andrew Pines
    TI__Intellectual 2600 points

    Hi Andrew

    TAS5755M is an old device, some describe at datasheet is not clearly, sorry we can't supply more information for you. You can click the GDE for help, there is a link introduce about DRC.