Force EQ

Well, I have a strange concern…
I have a song that I recorded on vinyl, but my amplifier had its EQ on when I was recording it to the file, so I’m wondering about this: If I were to do a general spectral analyze on both of those tracks, would it be possible to force the vinyl to have the same spectrum or a similar spectrum to the CD through equalization? I tried to do it manually, but it didn’t work very well, and it took a lot of time. What could I do?

Could you record it again?

Well, if it would be faster than waiting around for something to be made, I guess I will.
I guess I was just wondering if anything was made or could easily be made that would do it.
It’s just that I recorded the record being played for the first time, so it may not be as clean, but I don’t think it would be too bad.

I guess I was just wondering if anything was made or could easily be made that would do it.

No. Equalizers are not one thing. They are designed differently depending on how much money the designer had to work with and how much sound damage is to be tolerated. Trying to “undo” equalization between two different machines – even if you knew what the curve was, it almost impossible.


Apple’s Logic Studio has a “Match EQ” plug-in

There are others out there that claim to do this. I’ve seen them, but can’t seem to find the right search terms to find them again.

None are free, as I recall.

– Bill

PS: Here’s another one:

Funnily enough this came up earlier today:

Now I’m thinking about the export function on spectral analyzer and the import function on the EQ. If I could write a script to find the difference between two spectrums and convert that into the EQ format inverted, it would be possible to roughly replicate that function. Are there any hidden challenges in this?

Great minds think alike …

That sounds perfectly doable.
I expect it would work best (and not so slow) with a small FFT size in “Plot Spectrum”, possibly even averaging values to create a smoother curve. You would probably not want to try to reproduce occasional spikes that may be in the spectrum, but rather reproduce the overall contour.

Yes, it’s doable. I did it with a spreadsheet, and once you have the spreadsheet formulas set up it takes a few minutes to generate the custom EQ XML file and apply the EQ. It works well if you are comparing the identical portion of a song from an LP capture and a CD, assuming the CD has not been remixed or heavily compressed. I don’t know how well it would work trying to EQ different songs.

It seems that this would be relatively easy to implement within Audacity. Plot Spectrum is already generating the data. I think it would involve a three step process: capture the spectrum of sample 1; capture the spectrum of sample 2; name and save the custom EQ XML file. Then import that file into the Equalization effect using the new “Save/Manage Curves” dialog in 1.3.13.

  • Bill

I wonder what that’s going to sound like.

The original problem is caused by an electrical equalizer and it’s going to have different phase and group delays that the digital one isn’t. Yes, I know this is going to be one of those ‘some people hear it and some don’t’ problems, and the comparison tools will certainly help, but the poster is worrying about the wear between the first and second playings of a vinyl record, so we’re not talking about gentle averaging errors. We’re talking about making all the errors vanish.


Then lies the question:

Which is greater, the minor loss in quality with the vinyl, or the possible not-good-enough-ness of the spectral stuff…

By the way, when I labeled this “Force EQ”, an equalizer that automatically makes frequencies the levels you set them to rather than relative to their previous values; for some reason I thought that would be what I needed. It might make a cool dual functionality of the spectrum thing, but it would probably bring out noise in places where there are not too many other things, and re-introduce subsonic trash if I’m not careful.

P.S. If you read the thing on me not knowing how to clean vinyl, that was the routine that my dad suggested I use, mostly.

There’s the rule of recording it right the first time because you can’t actually fix this stuff in post production. You can glue patches on it, wire some of the bits back on and wrap rags around some of the more gaping wounds, but you can’t ever get back to zero. I am without question in the record it again camp.

And I wouldn’t do it with that record. Choose another record and take it through the whole process beginning to end. Write down the errors and fix problems. Then, when you have the pipeline stable and predictable, transfer the real thing. If you don’t have any ratty records, go out and buy one at a garage sale.


Good advice.

I’ll try ripping some of my stuff so old it doesn’t matter how many times its been played.

so old it doesn’t matter how many times its been played.

Yes, but remember there is still that “letting vinyl rest” thing. It takes a vinyl record an hour or more to recover from the stress of having been played once. We are talking about dragging a diamond knife over plastic

Also, much has been written about removing vinyl noise.