## Cleaning up 78 transfers

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Reply #49 –

I've got Capitol, Pathe, Odeon, 4 kinds of Columbia, Okeh and severael more that don't appear anywhere in that software. Yes, I did actually install it. What do I do about those? How do I begin to know which one to choose.

If they are on that long list, and if the list included both turnover frequencies (which it doesn't), you'd just type those two values in the high and middle values of a custom filter. Where LF shelving is specified, type that in as the lower number. Where it's not specified just use 20 (or 1). Job done.

Unfortunately, one of the turnover frequencies is missing from all entries in that list! So, I'd look at the values for the type you have, and pick whichever standard curve is closest.

There must be a simple calculation to figure out the exact correct turnover value from the 10kHz cut value, but that's beyond me. It's something *like*...

treble_turnover_frequency = 5.6 - (0.25 * cut_at_10kHz)

...but that's a pocket calculator guess, not a proper formula.

I can give you MATLAB code to generate the curves from the turnover values though. I've just found the formula in some old EE notes. It's the a=... part below...

% riaa2.m - plot amplitude against frequency of RIAA filter

f1=50; % lower bass turnover / "low frequency" (if none use 1)

f2=500; % bass turnover / "middle frequency"

f3=2121; % treble turnover / "high frequency"

f=1:20000; % set up array with frequencies 1-20k to calculate response at each frequency

% calculate response

a=(1+i.*f./f2)./((1+i.*f./f1).*(1+i.*f./f3));

a=a./abs(a(1000));

% uncomment this line to calculate inverse curve...

%a=1./a;

% plot amplitude of result in dB (using 20*log10) on log frequency scale (using semilogx) from 20-20kHz

semilogx(f,20*log10(abs(a)))

xlabel('frequency / Hz')

ylabel('amplitude / dB')

axis([20 20000 -30 30])

...but you don't need it. Unless you really want to program the curve into audacity.

Be prepared for some records not to match the listed curve at all. Sometimes labels licensed recordings from other labels, or went to different studios for one session. In this case, the named curve for that label could be completely wrong for that recording. If it sounds completely wrong to you, have confidence in your ears, and try another. At this point, it really is educated guess work. Trying increasing or decreasing the turnover frequency until it sounds right.

Hope this helps.

Cheers,

David.

P.S. forgotten.