Making an Audio Frequency Meter

Discussion in 'The Projects Forum' started by Sparky49, Jul 30, 2012.

  1. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Hi everyone,

    As you probably know I play the bagpipes in a band, and a large amount of time is spent tuning the instrument - in perticular the drones. The emit a single tone and must be at a set frequency.

    Subtle changes in temperature, air pressure and humidity changes where these drones tune, so it becomes a hassle to tune them often by ear. To get around this, a few companies have made frequency meters - held beside the drone, they display the frequency and you tune the drone to your desired frequency.

    However, they can charge around £600 - which seems rediculous to me, becuase they just a moving coil. I've not seen what's inside but I don't imagine it justifies £600!

    I've decided to build my own - and have searched for circuits, however, I would appreciate it if you guys could check their design.

    The first is here:
    http://electroschematics.com/3054/sound-frequency-meter-circuit/

    I presume at signal in, I can just put a microphone there?

    Many thanks for your time,

    Sparky
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I would recommend doing this in software, to make "an app for that". For guitar tuning, for instance, you can already get free apps that will detect which string you're likely trying to tune and adjust the display to help you tune to that note. This means you don't even have to take your hands off the instrument to adjust the tuner. Of course you need a laptop or smartphone, but no other dedicated hardware.
     
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  3. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    I would so be up for that - but I'm concentrating on getting LEDs to flash at the moment. ;)

    Cool for a future project, but I'd love to give it a bash with components.

    Thanks for your advice though. :)
     
  4. bertus

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    Apr 5, 2008
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  5. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    However, I'm rubbish at programing, and if I used some of the ready made programs, I'd feel like I'm cheaping a little. :)
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Well, if you want to build one, I'd look for a digital solution. A decent tuner needs a decent clock as a reference, so you'll need a quartz crystal oscillator. The circuit you posted "digitizes" the sound for counting the peaks but then converts the result back into an analog signal for the meter.

    This means the calibration of the meter and the stability of that calibration will be a limiting factor on your tuning. In short, it won't work, IMHO. It might help get close, like with a guitar string so out of tune you can't even tell what octave you're on, but your own ear will be far more accurate for fine-tuning. The "tuner" response may drift around more than the bagpipe itself does.

    I think smart folks here could help you process an all-digital signal into a useful readout. My favorite tuner display is a horizontal strip of LEDs that stabilizes when the frequencies match. Very easy to use even under chaotic situations (ie., on stage).
     
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  7. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I know you want to build something in hardware, but I use the "Audalyzer" Android application. It's a versatile, configurable audio spectrum analyzer. The one big limitation is the frequency response of the microphone and amplifier in the phone but I could plug in a better microphone and since we're interested in frequency alone, much more than accurate representation of relative amplitude across the spectrum, it should work in your case.

    What frequencies do you need to work with?
     
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  8. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Everything is tuned to A.

    The chanter's Low A is tuned about 469-472 Hz, the tenor drones tune one octave below, and the bass one octave further.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Huh, never knew that. So, a bagpipe can't normally play with a piano or guitar (A=440)?
     
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  10. JohnInTX

    Moderator

    Jun 26, 2012
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    Chromatic clip on tuners with switchable vibration sensor or microphone. I've used the SN-2 to tune guitars, basses, horns etc. successfully. Tunes fine down to C2. Maybe less sensitive below that. Can adjust A from 415-466hz as well as up to 4 calibrated 1/2 steps down for b instruments. About $12.00 on Amazon.
     
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  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    So a fairly narrow range, from ~100Hz to ~500Hz?
     
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  12. bertus

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  13. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Nope Wayne, we only have one octave to play around with, GABCDEFGA.

    To make matters worse each note must be tuned, because unlike other wind instruments, each note can change at a different rate. To do this we use electrical tape! :)

    Thanks for the pointer John.

    Perhaps I should make it clear that I'm not interested in an accurate tuner - just something which is precise.

    If I end up using a meter, I'll only use values as a reference point.
     
  14. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    @Bertus, relative to a true A (A=440) we play at about 442-445, but we add 27 to get actual pitch.

    @KJ6, yes, and we can't even change our drones!
     
  15. KJ6EAD

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  16. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Yes, they look pretty, but the problem with the bagpipes is that they are not chromatic - that is they don't have an equal distance between notes.

    Which kinda rules out tuners like that, because whilst our C might be in tune in real life, the chromatic will show it as a flat C#.
     
  17. bertus

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  18. KJ6EAD

    Senior Member

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    Those two Snark models also limit the A calibration to 466Hz. :(

    Maybe someone (hint) should tell Snark to make a pipes model. It would probably be a small software change for them to open up a whole new market segment.
     
    Last edited: Jul 30, 2012
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