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Fractional Voltage Controlled Multi TAP Delay ADAU1466

I'm quite new to AD DSP and have recently acquired a 1701 evaluation board and a 1466 Evaluation board. I'm trying to use the Fractual Voltage Controlled Multi Tap Delay, but I can't get my head around the control input (samples, percentage?) and  the data format to be used? I can't find anythig in the documentation.

I'm using the SIGMA Studio 3.16 Beta Version of the program.

I'm trying to control the delay time of six taps with one ADC.

Ant help is much appreciated

  • Hello wolft,

    I will get you started. I am running out the door way past quitting time so excuse the short response.

    This is basically how you would use it.

    The control input should be in samples so you will probably have to scale it. I attached a very quick project I threw together but then realized you are using the 1466. So this is done with the 1452 DLL. It will run on a 1466 so you can test it.

    Use the readback cell to give you feedback on what the AUXADC is sending out or after you scale it.

    Send your project next time so we can see what you are doing and so we can make better suggestions.

    Oh, and here is a link to the Wiki help page:

    Dave T
  • Hi Dave

    Thanks for the quick response. Your example works on the 1466   I was using the Fractional Delay which requires an input between 0 -1 (8:24 numerical format) which changes the delay length from 0 - 100 %.

    I had to do a 14 bit << shift on the ADC output to get it working.

    Thanks again for your help. Quite to lot to take in for me, and it's good to know that there are people out there willing to help.


  • Hello WolfT,

    Glad you got it working. In my hurry I was not able to verify if the cell wanted an integer relating to the number of samples of delay to use or if it needed a percentage from 0-1. So I am glad you figured it out and the shifting of the AUXADC is exactly how it should be done. Bravo!

    This is a pretty cool capability this cell gives for adjusting the delay.


    Dave T

  • Hello WolfT,

    I did some research and testing of this cell and the multi-tap cell that is not fractional. So I feel the need to detail some of my findings here and give some examples for you and for others who may read this post.

    You are correct that the Fractional Multi-tap Voltage Controlled Delay cell takes in a number from 0-1 as a control input and it will set the delay as a percentage of the maximum delay time set in the GUI.

    For the non-fractional version this is not true. That version, the Multi-tap Voltage Controlled Delay takes in an integer number that is the number of samples to delay by.

    For both, when using an external potentiometer, it is advised to use the software debounce cell in the GPIO library. This will prevent the delay time from dithering which causes a distortion as the delay changes the length of the delay.

    For the non-fractional version, you do not want to send it a number that is larger than the max number of samples set in the GUI. So using an externally controlled volume control to divide down a DC input will perform this job quite well. Then you can also use the slew feature to smooth the rapid pot changes and make a much more pleasing output with much less distortion when the delay time is changed. It is actually a rather cool sounding effect.

    I have attached the two projects for reference. They will work on the newer style of evaluation boards that have two AUXADC pots on the PCB. The older style you will have to solder wires from the evaluation board to an external pot.


    Dave T
  • Hi Dave

    Thanks for the details how the delays work and the tip to use the debounce. Really helpful.

    I'm trying to emulate a certain 'old' effect unit (ADA STD-01) and getting pretty close. I want the delay time to be modulated by a slow sin wave (0.1 -10Hz) in which case the debounce doesn't work .  Caused by the modulation I get some distortion, so I guess I have to play around a bit more with the available modules. I chose the fractual tap delay module instead of the 'normal' tap delay as I thought it would do some sort of interpolation when changing the delay time and therefore does not produce the same amount of distortion? Anyway having fun playing with the ADAU1466 (and the 1701).


  • Hi Dave,

    I am currently working with the very same delay cell on an ADAU1452 chip. I was able to control the tap delay (2 taps) using the DC input entry, but the result wasn't as expected. Typing in 0 and 1 outputs a non delayed signal and a max delayed signal, respectively (as expected). But typing in 0.5 don't give me half the maximum delay time. Instead, it outputs the same result as if I typed in a 1. I haven't got the chance to attach my project file since I'm out of office, but it is the exact diagram as the one showed in the documentation (the one example with 0.2 and 0.4 DC input as a control signal). Do you have any idea on what may caused this? My DC input cell number format is 8.24, if that helps. Thank you!