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The simplest audio delay in the world

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by scrawny git, Oct 9, 2008.

  1. scrawny git

    scrawny git New Member

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    I'd like to have a go at building some very straightforward audio delay circuits. No variables, just a fixed time delay (upwards of 1 second) which I assume is achieved with resistor values, and continual one time playback. Does anyone know a good source of simple schematics for this?

    So far I've found this one:[​IMG], which looks nice and easy once you have the right chips.

    Any ideas/experience?
     
  2. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Are you going to use 1 Bit ADC?

    Audio can be a very complex waveform and it is no trivial feat to time delay it.
     
  3. scrawny git

    scrawny git New Member

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    I take your point, but I am not necessarily interested in reproducing the sound with any attention to fidelity. Could I not make a test circuit with a 1-bit adc and replace it with a higher bit one if I can get it to do what I want? (I am assuming bits and £s are closely connected)
     
  4. dave

    Dave New Member

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  5. blueroomelectronics

    blueroomelectronics Well-Known Member

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    A 1 bit ADC means its a form of PWM input to a digital output.
    http://www.cs.tut.fi/sgn/arg/rosti/1-bit/

    I would suggest something more straight forward if you're studying electronics.
     
    Last edited: Oct 9, 2008
  6. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Yes, you need some sort of serial digital bit stream. That's what the note "Using a 1-bit oversample ADC" on your schematic means. The "Audio Input" is from the A/D converter. If you just feed audio directly into the circuit, you will get something that has little resemblence to the original audio.

    1-bit does not mean low fidelity, it just means the information is in a single bit-stream. This can be a 1-bit ADC that gives a PWM signal as described by blueroomelectronics. You could also use the output of a standard A/D converter that has a serial output. If you wanted to listen to it after the delay, you would have to convert it back to analog by passing the output to a serial input D/A converter.

    A PWM signal can be converted to analog by passing the bit stream through a low-pass filter and amplifying the filtered signal, since the signal has an average value equal to the orignial digitized signal. For best response a high order filter is needed, but a simple 1-pole filter will give a useable signal if you don't need maximum fidelity.
     
  7. kchriste

    kchriste New Member Forum Supporter

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    Here is a schematic that is similar to the one above and uses ancient components that may be hard to find:
    http://www.armory.com/~rstevew/Public/SoundSynth/Reverb/ddl.htm
    There used to be analog bucket brigade chips such as the MN3011 or SAD1024, designed specifically for the generation of audio delays, but they are long obsolete. A microcontroller with an ADC, PWM/DAC and a decent amount of RAM (32K) would be one way to do it.
     
    Last edited: Oct 9, 2008
  8. scrawny git

    scrawny git New Member

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    I have found the attached datasheet/schematic for a simple enough looking circuit based around the MX609. This looks easier than the schematic i found which uses the MN3011 replacement: NJU9702, and it gives longer delays (up to two seconds). So now you're going to tell me MX609 is obsolete? or does this look like a possibility? If so then what's the thing marked 1,024 MHZ
     

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  9. crutschow

    crutschow Well-Known Member Most Helpful Member

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    That thing is a 1.024MHz quartz crystal. XTAL is an abbreviation for crystal. It causes the oscillator in the MX609P to oscillate at a precise frequency. The MX609P data sheet should have more info on that.
     
  10. Roff

    Roff Well-Known Member

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    The circuit is a simple delta-sigma ADC, but there is an error in the schematic. IIRC, this was originally published in EDN Design Ideas, and was subsequently corrected, but errors live forever on the Internet.
    With the correction (see attached), it will work as a crude ADC, and audio (not another ADC output) is the input signal.
     

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  11. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Ron is right of course. Should have taken a closer look at the schematic to realize something was wrong with the original.

    Do you know what clock frequency was recommended?
     
  12. Roff

    Roff Well-Known Member

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    I don't remember the clock rate. I ran a sim on it this morning with Fclock=100kHz, and RxCx=100 usec. It looked OK to around Faudio=5kHz. I didn't try running the sim on a WAV file and then playing back the result (which you can do with LTspice by jumping through a few hoops).
     
  13. crutschow

    crutschow Well-Known Member Most Helpful Member

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  14. scrawny git

    scrawny git New Member

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    I have now built this circuit:
    [​IMG]

    and it works, and delay times are adjustable by the value of R

    BUT

    I would like to only hear the delayed signal, and not the original sound, does anyone know how I might be able to add a dry/wet control? or do i need to build a separate timer circuit which switched the audio on after x milliseconds?
     
  15. crutschow

    crutschow Well-Known Member Most Helpful Member

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    The second schematic in the PT2399 data sheet is for a surround/delay application and that should do what you want.
     
  16. valvusmusicus

    valvusmusicus New Member

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    Multi tap delay question

    Hi Scrawny git and others
    In relation to your MX609 circuit-how would you make this a multi-tap delay, like the MN3011 with 6 taps or the 3012 with 3 please

    Dense of BH22
     

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