Force EQ

[samspots]

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?

[steve]

Could you record it again?

[samspots]

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.

[kozikowski]

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.

Koz

[billw58]

Apple's Logic Studio has a "Match EQ" plug-in

http://documentation.apple.com/en/logic ... tasks=true

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: http://www.voxengo.com/product/curveeq/

[steve]

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.

Funnily enough this came up earlier today: http://forum.audacityteam.org/viewtopic ... 22#p128588

[samspots]

Hmm...
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?

[Trebor]

Hmm...
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.

Great minds think alike ... http://forum.audacityteam.org/viewtopic ... 28&t=43958

[steve]

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.

[billw58]

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