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Test tones - what frequency?

Discussion in 'AV Receivers & Amplifiers' started by bbanduser, May 24, 2004.

  1. bbanduser

    bbanduser
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    I have a SPL meter which has only got A rating (the one from CPC.CO.UK). Now the A rating requires quite a lot of correction,but all of these are based on the frequency.
    So my question is - how do I know what the frequency is from the test tone? I will have to apply the correction based on the frequency, so knowing the frequency is very important.

    Or is there another way of going about it?
     
  2. Reiner

    Reiner
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    It depends where the test tone comes from or how it was implemented. I think my Yamaha outputs white noise, that is a mix of tones over the entire (?) frequency band.
     
  3. bbanduser

    bbanduser
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    If the frequencies are across a big band, then how do people apply corrections to the dB level based on this?
     
  4. Mylo

    Mylo
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    Good question.

    I calibrate my setup using the THX optimiser supplied free on the 'Monsters Inc' dvd.
     
  5. eviljohn2

    eviljohn2
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    I think white noise has equal amplitude across the audible bandgap whilst pink noise is adjusted to compensate for the human losses at the extremes.

    All the THX Optimiser discs I've got expressly say that they're not designed for adjusting channel level and that internal test tones should be used. :confused:
     
  6. Mylo

    Mylo
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    really??? :confused: I use my work Sound level meter with the THX disc and it seems to work ok.

    Edit: anyone with a Marantz SR4200 will know how much of a pain the test tones are to use and adjust, too much effort for Mylo. :blush:
     
  7. eviljohn2

    eviljohn2
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    That's using Evil Dead, T2 and Monster Inc. in fact. It's in one of the explanation screens because there's no actual test for it - it just tests that the speakers are functioning.

    Not that I could hear any difference between those and the internal tones from my Denon 1802. Mine are all done by ear so it's hardly a precise methoed either way ;)
     
  8. rscott4563

    rscott4563
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    For what your wanting, your best bet would be to make your own CD with specific frequency test signals on it.

    I can email you a zip file with a collection of mp3's, each one lasts 10secs with a fade in and fade out, there are 66 going from 10Hz to 18kHz

    These are designed for doing freqency sweeps of a room to get a frequency response graph, but by using just one, say 500Hz it should give you what you want.

    You just need to convert them to .wav and rip them to a CD

    Let me know..
     
  9. eviljohn2

    eviljohn2
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    I wouldn't recommend using a single toned frequency because if it happens to be a modal frequency or have some other odd interaction with the room it'll mess up the settings.
     
  10. rscott4563

    rscott4563
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    But thats exactly what was asked for, without using a set frequency how will bbanduser be able to apply the right corrections?

    You could take your measurements 3 or 4 times using a different frequency each time, this would mean you should be able to tell if one is completely different and just ignore it..
     
  11. eviljohn2

    eviljohn2
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    That was going to be my next suggestion. :) Using a single frequency is just asking for trouble really but using several and some common sense should resolve most easily fixed problems.
     
  12. bbanduser

    bbanduser
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    rscott4563, if I have a CD with say a few frequency tones as tracks, how will I be able to get the output from only 1 speaker at a time?
     
  13. rscott4563

    rscott4563
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    You can either disconnect the other speakers and just plug in the one you want to test or if your amp has the ability you should be able to just set speakers to off and just set one at a time..

    To be honest I'd forgot about getting the tones from one speaker at a time, but the above should work fine.
     

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