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audio application question — Parallax Forums

audio application question

guydbguydb Posts: 29
edited 2007-07-05 08:15 in BASIC Stamp
hi,
I started working on an experiment that should end up being a bare bones stamp controlled digital audio mixer. just for starting I used a DS1804 (I have a couple at hand) and I got way more hum than I could live with (a very simple one pot fade in fade out test). Any ideas how to get rid of the hum?
thanks
guy

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-04 16:31
    You need careful isolation of audio and digital signals, extra filtering of supply voltages. These digitally controlled pots are intended more for setting voltage or current levels than controlling low level audio signals, so you may need a voltage controlled amplifier whose gain is set by the digital pot.

    Have a look at en.wikipedia.org/wiki/Voltage_controlled_amplifier.

    Also look at this application note from Dallas: www.maxim-ic.com/appnotes.cfm/appnote_number/161.

    Post Edited (Mike Green) : 7/4/2007 4:45:35 PM GMT
  • guydbguydb Posts: 29
    edited 2007-07-04 16:38
    thank you,
    that makes perfect sense (and I was myself thinking in that direction, but the naive optimist in me was hoping for a very simple solution)
    guy
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2007-07-04 16:47
    Guy,

    Don't ever lose your naive optimism! It can take you to interesting places. If my own projects didn't begin with naive optimism, most probably wouldn't begin at all! wink.gif

    -Phil
  • guydbguydb Posts: 29
    edited 2007-07-04 18:16
    there is actually another project where the VCA won't help, it is where I want to replace an analog pot with a digital one within an existing analog audio circuit, not necessarily to control volume
  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-04 18:39
    Do read the application note from Dallas. It talks about issues like biasing the audio to keep it in the 0-5V range.
  • pwillardpwillard Posts: 321
    edited 2007-07-05 02:02
    You might want to take a look at how this guy did his...

    http://www.twistedpearaudio.com/joshuatree/jt.aspx
  • guydbguydb Posts: 29
    edited 2007-07-05 08:15
    wow, I'll keep it as plan B, but it certainly will yield clean results, thanks.
    and the maxim application note on the 1802 (especially the Wheatston Bridge concept) is indeed an enlightening read.
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