Submit your EQ Curves

Special Interest Groups Audio Processing
35

Hi Irish

Martyn has commented on Bugzilla:

The idea of “78EQCurveGen.ny” sounds excellent but the implementation may not
be. The spreadsheet at
http://forum.audacityteam.org/download/file.php?id=1662
(from > https://forum.audacityteam.org/t/audacity-1-3-3-presonus-inspire-now-much-love/182/1 ) is
almost certainly flawed (it doesn’t match my spreadsheet or any other curves
I’ve seen on the web.
Internet, TV en Bellen | Online.nl > looks like
a good source for reference, or the usual wikipedia.

I think we will still want one (or a few) “generic” electrical 78 rpm curves for the default curves included in Audacity. This is currently the default curve that “78EQCurveGen.ny” produces (normalization to 1000 Hz= “on”):

<curve name="Generic electrical 78">
<point f="20.0" d="19.711498"/>
<point f="25.0" d="19.390201"/>
<point f="31.5" d="18.912903"/>
<point f="40.0" d="18.224799"/>
<point f="50.0" d="17.375757"/>
<point f="63.0" d="16.277917"/>
<point f="80.0" d="14.926615"/>
<point f="100.0" d="13.501542"/>
<point f="125.0" d="11.964888"/>
<point f="160.0" d="10.193469"/>
<point f="200.0" d="8.580567"/>
<point f="250.0" d="7.005806"/>
<point f="315.0" d="5.463814"/>
<point f="400.0" d="4.012324"/>
<point f="500.0" d="2.817063"/>
<point f="630.0" d="1.748690"/>
<point f="800.0" d="0.798759"/>
<point f="1000.0" d="0.000000"/>
<point f="1250.0" d="-0.781918"/>
<point f="1600.0" d="-1.713087"/>
<point f="2000.0" d="-2.680988"/>
<point f="2500.0" d="-3.809318"/>
<point f="3150.0" d="-5.159826"/>
<point f="4000.0" d="-6.736534"/>
<point f="5000.0" d="-8.347118"/>
<point f="6300.0" d="-10.122190"/>
<point f="8000.0" d="-12.039001"/>
<point f="10000.0" d="-13.881058"/>
<point f="12500.0" d="-15.756427"/>
<point f="16000.0" d="-17.856488"/>
<point f="20000.0" d="-19.769572"/>
</curve>

In fact it may be that 78 rpm curves could be shoehorned into three broad groups.

  1. like your default generator curve, Victor (1938-47), MGM, Columbia US (1938) in the “78’s” section here

  2. flat in middle frequencies - “EMI 78” and “Decca FFRR 78” in the curves issued with 1.3.12, plus Capitol, early Decca, Columbia (US 1925 onward), FFRR in the same graphs)

  3. flat in lower frequencies - Columbia (English), Brunswick, Parlophone in the same graphs)

Would this be reasonable, instead of the larger number of 78 rpm curves we have now? Maybe it would be better to describe the curve characteristics than try and give manufacturer’s names/dates to these curves, given how much variance there was?

Other points:

  • We can’t prevent 78EQCurveGen.ny creating an empty track, I take it, after writing the curve?

  • Until 78EQCurveGen can append to the xml file, I think it would be more useful if the file name it wrote to was the same as the EQ Curve Name. Then you can write multiple curves at (more or less) the same time instead of one-at-a-time


    Thanks


    Gale