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TAS5717 / TAS5719 DRC behavior and configuration problem

Frederic Roskam
Prodigy 50 points
Other Parts Discussed in Thread: TAS5717

Hello,

I urgently need to figure out the precise behavior of the dual-band DRC inside this TAS5717 amp.

First, from what I've read in this forum (and unlike what the datasheet says) the ratio and offset are fixed for a limiter-like behavior. What are those fixed values? Infinite ratio and 0 offset?

Then, and most importantly, how to tune such limiter? The compression gain is applied before the level detection (SLOS655A p4), a bit odd to me. So a soon as the input level goes above the threshold (and with given attack time constants), the compression is applied and the input level gets lowered to a value close to that threshold. With a broadband signal, this is likely to go below the threshold at times and therefore will release the compression, so the limiter will oscillate constantly between those two positions. Am I correct?

Finally, if the above is correct, I could not find a set of "softening filter" / "attack" / "release" that produces a nice sound output. Do you have typical values for the lower and upper band (x-over at 300Hz) with music?


Thank you!

Best regards,

Fred

  • 0
    TI__Guru**** 189401 points

    Hi, Fred,

    Sorry for the confusion. I've asked my colleague to look at this with you. Unfortunately, he is pretty swamped at the moment. But, he should be able to get back to you in a day or two. 

    D2

  • 0 in reply to Don Dapkus
    TI__Mastermind 34775 points

    Hello Fred,

    I will work with you on resolving the DRC issue. I should have an answer tomorrow. Please provide your application PVDD, speaker load and desire power you want the DRC to limit. 

  • 0 in reply to Damian Lewis
    Prodigy 50 points

    Hi Damian,

    Thanks for picking up the issue. I have a PVDD of 12V for a 8-ohm load. Desired power is ~8W. The intention is to apply a large bass boost in the biquad section, the limiters protecting the output with a short attack time and long release time.
    Please advise

    Regards,

    Fred

  • 0 in reply to Frederic Roskam
    TI__Mastermind 34775 points

    Fred,

    With the your current setup conditions 12V PVDD and 8W in to 8-ohms load, the output is already supply voltage limited. The output is 5-8% THD+N at 8W with 12V supply rail, so setting the DRC for 8W will minimize further clipping, but wouldn't resolve the 5-8% distortion that exist at 8W due to the supply rail. In order to get a cleaner low frquency signal using the DRC, you can try the following:

    • Lower DRC threshold (max output power) < 1% THD+N (~7W)
    • Increase supply voltage to get < 1% THD+N at 8W
    • Use 6 ohm speaker loads
  • 0 in reply to Damian Lewis
    Prodigy 50 points

    Hi Damian,

    Thanks.
    Now let's assume I want to reduce the output power to 7W or below, using the DRC settings for the lower band only, what are the typical settings (lower band = 50-300Hz)?

    - Softening filter rate

    - Attack rate

    - Release rate

    Thanks.

    Frederic

  • 0 in reply to Frederic Roskam
    TI__Mastermind 34775 points

    Fred,

    One more thing I would like to mention in addition to my other recommendations. When playing a lot of low frequency content having sufficient bulk capacitiance on the the supply helps stablize the supply and keep it from sagging/drooping. When the supply droops it will reduce the signal headroom and depending of how close the signal peaks are to the supply voltage, it can introduce more distortion.

    Are you using the GDE provided forTAS5717/19? If so I will recommend setting the threshold to 7W then listening to music with low frequency contents and use the GDE to tuning it to your taste/liking.

    If you have a particular track you use for tuning that you would like to share with me I can listen to it and provide suggestions.

  • 0 in reply to Damian Lewis
    Prodigy 240 points

    With regards to the TAS5717, is there a description of the limiter settings and their definitions? The spec sheet leaves much to be desired and many parameters undefined. The EVM spec only has snap shots of the GDE interface.

     

    For example, where is "softening filter" defined? In the spec (page 30) there are parameters T, K and O. with "see GDE software tool for more description"  Then figure 41 (page 30) has alpha and omega defined pointing to a "Energy Filter" block. In the GUI, we have sliders no reference to alpha or omega.

     

    On another note the dual band DRC, what should the crossover filter do? I assume split the signal to two different DRC control blocks. On my board it acts like a generic high pass filter for the whole system.

     

  • 0 in reply to Mark Trainer
    TI__Mastermind 34775 points

    Hello Mark,

    Please review the attached presentation on TAS57xx audio processing blocks. Let me know if it answers your questions or you have additional questions.

    7268.TAS57xx DAP Training 2014.pptx