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Matching stereo eq channels.
Old 4 weeks ago
Gear Addict
Matching stereo eq channels.

So just for the sake of debate and learning I like to pose questions to see if there are better ways of doing things.

So even on a super expensive EQ like a GML 8500 the components are not matched absolutely. So if you were setting up an eq that you wanted to be the same on L R and were just matching the positions by eye they would be different.

This what I am doing.

Without the eq in I match the levels of the channels. I note down the required settings. Then I put the settings all back to 0.

I take the first band and set it in isolation then match the other channel to it. Then I move onto the other bands one by one.
That is a quick way to do it but does not take into account the Q width.

I don't own an oscilloscope, but if I did I guess you would also be able to see the bandwidth of the Q.
Old 4 weeks ago
Gear Addict

I think EQs like the GML use stepped controls so you can have the same thing going on both channels. As for the method you're describing. I think you'd have better results just using your ears and level matching any changes you make with an SPL meter.
Old 4 weeks ago
Lives for gear

as i mentioned in your related thread, i'm using pink noise for most tests - maybe i should also mention that i'm using rational acoustic's smaart to analyze and dk audio goniometer/level meter. but of course a simple tone generator and a multimeter will do in most cases!

i don't have to deal with my analog gear very often these days - and don't really miss it: one of the reasons is that i hardly ever need to measure things in the digital domain, so most measurements i'm doing are about speaker response/phase relationship.
Old 4 weeks ago
Lives for gear

If you suspect your EQ has uneven outputs you should use a calibration disk and either a DB meter or Frequency analyzer to calibrate your frequency bands.

I still have a calibration disk I bought years ago. you may be able to find one free on line. It typically has test tones for each of the EQ bands and Pink/White noise files which test them all at once. Here's and example

You can also download a frequency generator that produces these fixed tones. Wavosour is one.
I have another free one which is excellent for this purpose but I cant remember its name at the moment. If I remember I'll find iyt for you, otherwise KVR should have some.

Foe a Frequency Analyzer you could use Voxengo Span which is a Free stereo frequency analyzer.

The way you'd test a hardware EQ is to use the frequency generator to output a -6dB signal from your interface and feed it into your EQ. Feed the output of the EQ back to your interface on a new channel and put The frequency analyzer running in real time. Then you'd simply change frequency bands, compare the track volume level and see if each frequency band puts out the same volume level for each band. You can use the frequency analyzer to see if the peak frequency is accurate.

Graphic EQ's can be off a bit but because the bands overlap its not usually off by much unless the pots are dirty or caps are getting old.
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