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volume/frequency activated gates/triggers

Discussion in 'Audio' started by darren adcock, Jul 23, 2018.

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  1. darren adcock

    darren adcock

    463
    34
    Sep 26, 2016
    Hi all, I've been asked to make a device which allows a rapper to produce gates/triggers to interface with midi equipment. After an initial discussion we decided that we could use certain or a series of volume and frequency windows which would activate the gates/triggers. This would all be derived from vocal's via a microphone. It is preferred that the circuit runs off batteries.

    Usually in a project I head straight in and then have to back paddle when i get stuck. So thought I'd try and start with a post of how I think i need to achieve this, see what folk here think (It's new ground for me) and try and get the circuit drawn before i start plugging things in.

    How I've imagined things so far;
    For frequency detection
    - SM58 - Pre amp/buffer - frequency to voltage converter (LM331) - window comparator - gate buffer with a comparator input leading to 40106's for both trigger and gate out ( this circuit is from MFOS here http://musicfromouterspace.com/analogsynth_new/HOT_TIPS/PDF/gatebuffer20090923_assembly.pdf )

    For dB detection
    Is the same as above but the frequency to voltage converter is changed to a single op amp amplifier to amplify the mic signal into a larger voltage range
     
  2. kellys_eye

    kellys_eye

    4,276
    1,146
    Jun 25, 2010
    Amplitude is 'easy' - any circuit used to indicate signal level (LM3915/LED bar) can be 'tapped' to take off a switching signal.

    Frequency is less easy - you have to consider the frequency and the bandwidth but it's still (fairly) easy to achieve and, 'back in the day', the NE567 was commonly used.
     
  3. Alec_t

    Alec_t

    2,822
    754
    Jul 7, 2015
    LM3915 is obsolete, but may be still available somewhere.
     
  4. darren adcock

    darren adcock

    463
    34
    Sep 26, 2016
    Ok thanks. I can find the NE567 quite easy and will look at related schematics today and try to understand the consideration needed of the relationship with frequency and bandwith (I understand the terms) in this application.

    In terms of amplitude, I'll follow your advice as makes my making much simpler! :)
     
  5. darren adcock

    darren adcock

    463
    34
    Sep 26, 2016
    Hey Alec, I can find it quite easy on ebay for cheap. :)
     
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