Guitar reverb and ADAU 1701

Hi There,  I'm using a ADAU 1701 to create guitar effects in my new product.  I have 3 sounds: Distortion, Chorus, and reverb.  The Distortion and Chorus sound great, but I can't seem to get the Reverb to sound anywhere near where I want it.  It seems the more delay time I add, the more "latency" it adds to the sound...

I have done some research on the web and some have said that this chip just does not have enough on-board memory to create a good sounding reverb... Is this the case?  Does anyone have any experience with this?  I'm running out of time on this product and really need to find an answer on this.

Thanks for any help,

Kevin

  •      Hello Kevin,

         Your research is quite correct, the -1701's 43 mS worth of delay memory isn't enough for a good reverb.  This is why there's no ready-made reverb block for this chip.  However, we can multiply the available delay by four with the help of a two "synchronous multiplexer" blocks.  By having the delay operate upon four versions of your signal, the intermediate delays add up.  The overall effect is still not up to professional standards by any means, but at least it's serviceable -- about what you might find in a basic karaoke machine.  I attached an example below, at least it's worth playing with.

         Best regards,

         Bob

    sync-mux.dspproj.zip
  •      Here's a similar arrangement which works on the ADAU1761.  There's no synchronous multiplexer for this chip, so here a homemade clock drives a standard index mux.  I tested this with the ADAU1761Z eval board and a podcast audio source.  Both this project and the above one operate by time-division multiplexing their main delay, thus multiplying the available delay time at a lower effective sample rate.

         The ADAU1761's low power requirement might make it ideal for self-contained stomp boxes, etc.  However, it cannot self-boot -- thus requiring a microcontroller to boot it as well as provide a user interface.  Sometimes I wonder why there's no "do-it-all" SigmaDSP, with  all of the following:

    • Built-in converters (4 each)
    • Self-boot, with GPIOs and Aux ADCs
    • A few ASRCs
    • Low power with sleep mode
    • 100 MIPS @ 48 / 96 / 192 K sample rates
    • 8 K data memory

         But I'm afraid this is not a perfect world.  I'd love to buy a Prius too, but I drive a beat-up Ford Focus.

    Reverb-1761.dspproj.zip
  • Looks like there is a built in reverb in ADAU1452.

  •    Hello neb,

       Absolutely.  With its 20K x 2 Data RAM, the ADAU1452 has plenty of delay available for a good reverb -- and its SigmaStudio stock reverb works well.  Yet the -1452 lacks built-in converters and isn't the best choice for a self-contained, battery powered device such as the clip-on guitar amp that's the subject of this thread.   In contrast, the ADAU1761's low power and internal converters makes it a neat analog-in, analog-out solution that applies well in a variety of applications.  And if low power is not a necessity, the ADAU1701 is even easier because it self-boots.  Striving to stretch the limited resources of either is in fact a lot of fun!

         Best regards,

         Bob

  • Thanks. Do you have an example also for distortion effect?