Is there a specification for phono amps volume control,
> for instance most phono amps have a 0-10 knob, so if
> I put in a signal into the phono input I get a Loudness
> out the speaker.
>
> Here's the background,
> I design and QC the manufacture of specialized
> microphones such as,
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>
> Recently I was asked to produce a specification as to
> db gain, distortion, stuff like that, but I found for this
> application the spec is subjective.
>
> You can review "loudness" here,
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> and read about the subjectivity.
You are right, the loudness is a bit subjectiv, if you some music. If you use a sine signal and measure the audio pressure level, or the relative change for knob position 0-10 in something like dBU or dB(SPL), and the distortion of the signal in THD or something similar, it is objective:
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The EAR has a built in distortion (filter) to accentuate
> the 2khz-4khz range that is subjectively agreeable,
> to test subjects.
Yes, this is the reason e.g. for dB(A), or the new standard ITU BS.1771.
So I'm wondering if there's some 'rule of thumb' spec to
> ratio amplification from 0,1,2...10?
You should read some basics about dB, first.