Author Topic: Recording level meter - scaling?  (Read 4254 times)

IanW

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Recording level meter - scaling?
« on: August 16, 2010, 09:56:42 pm »
Hello Paul,

Mainly out of interest, please can you describe how the recording level meter is scaled?  I'm guessing that it's not linear as once the level gets up into the high 90s it seems there are quite big steps between levels of 97, 98, 99 and clipping, for example.  (This is with VS 7.5.2 on Mac OS X, I should say.)

Actually there is a bit of a practical reason for asking - I have several records that cause my ADC to clip very frequently, and I was wondering whether the meter could help me estimate how much attenuation I need to add in the analogue domain.

Thanks,

Ian

Paul Sanders (AlpineSoft)

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Re: Recording level meter - scaling?
« Reply #1 on: August 17, 2010, 11:43:40 am »
Hi Ian,

Do you mean the meter or the slider? The meter is linear.  The slider probably is too, but as it is supplied by OS X and not us I cannot be certain.  But if you are recording from a USB device (as it sounds like you might be), there may be no slider.  Many of USB devices have no gain control.

If your analog gain control is calibrated in dB (as many are), you might find the following table useful:

    -1dB = 89%
    -2dB = 79%
    -3dB = 71%
    -4dB = 63%
    -5dB = 56%
    -6dB = 50%

Rgds - Paul Sanders.

IanW

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Re: Recording level meter - scaling?
« Reply #2 on: August 17, 2010, 06:19:07 pm »
Sorry, I meant the meter.  (My ADC is a FireWire device and the slider is fixed at 100%.)

Thanks for the info.

Paul Sanders (AlpineSoft)

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Re: Recording level meter - scaling?
« Reply #3 on: August 17, 2010, 08:02:44 pm »
OK, well, yes, it's linear.  Specifically, it looks at the peak digitised value about 40 times per second (i.e. -32767..32767, for a 16-bit device, taking the absolute value rather than the signed value) and displays that.  I'm not sure why you observe non-linearity.  I can't say I have seen this in my tests.

You're the second person to ask how best to adjust a manual gain control.  Perhaps the dB <-> percentage table belongs in the help file.

I haven't forgotten about composer/title/performer by the way.  Pressure of work.