An MIR analysis of real amp versus captures and profiles

Orvillain

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So some background.

Mel-spectrogram:

In short:
Studies have shown that humans do not perceive frequencies on a linear scale. We are better at detecting differences in lower frequencies than higher frequencies. For example, we can easily tell the difference between 500 and 1000 Hz, but we will hardly be able to tell a difference between 10,000 and 10,500 Hz, even though the distance between the two pairs are the same.
...
...
A mel spectrogram is a spectrogram where the frequencies are converted to the mel scale.
IE: It is a spectral representation of an audio signal scaled against the mel-scale, which more closely represents how human hearing perceives frequencies.

So Here's what I did:

First I normalised the audio files in the DAW, to minimize digital level differences (not the same thing as balancing signals using your ears!)

Then I took a mel-spectrogram of each file. I then converted the data from power-spectrogram to dB.

For each modeller signal, I added it to an inverted version of the real amp signal; essentially a polarity inversion that you would do with audio in your DAW, but against the mel-scaled spectrogram>dB representation.

And these charts are what you get.

1667042361121.png


Effectively, for each frequency band.... the closer to zero you get, the more accurate the modeller signal is to the original signal. Where the colour is pink or red, those are the biggest differences compared to the original signal.

So from a high-level macro view, I observe two things:

- The Kemper has consistent differences in the low frequency range.
- During the palm-mutes in my riff, the Kemper suddenly snaps back into "very accurate" from 15,000hz down to about 7500hz.
- But on the open notes in the riff, this doesn't happen. There are quite a lot of differences on those notes.
- Also on the palm-mutes you do see interspersed red chunks throughout the frequency range. This also happens with the QC.

If we zoom in on the lower frequencies:
1667042462498.png


It may look like a load of noise. But I'm seeing some patterns in there that are quite interesting.

There are far fewer dark red chunks on the QC lane (3rd lane if it wasn't clear) than the other two. Below 1000hz. So let's zoom in there....
1667042498085.png


So look at frequencies 0 through to 500hz. The colour-banding here should tell you about the accuracy of the signals versus the real amp.

The Kemper has a much higher base level of pink and red in the 0hz to 500hz, across the file. This shows that in that frequency range, the Kemper is less accurate than the QC.

So now for IK ToneX. Unfortunately I made the Kemper VS QC clips in 2021, and don't have the DI anymore. So this is a completely different riff. But it has loads of palm mutes, strummed chords, and ghost notes and such.

1667042634794.png


Ignore the amp line at the top - actually no, don't. What that is showing is that the inverted amp and amp data completely cancel each other out (constant stream of zero's in every single band) which means my analysis is doing the right thing.

There *are* differences of course. But fewer instances of bright red and super dark blue.

This isn't exhaustive. Can't be taken as a truth because of the limited dataset, but IK ToneX seems to be more accurate than both the Kemper and QC, on the surface of things.
 
Thanks, yeah I think that would be a fairer comparison considering the other units are using ARM+DSP chips for training vs a full blown desktop computer with modern powerful CPU+GPU.
Honestly, from experience the only difference ARM+DSP versus CPU+GPU would or should make, is simply training times.

The difference here is the Tensorflow engine that IK Multimedia are using in the background, and the algorithm they've written for it. If I am right, then Kemper doesn't use modern machine learning techniques, and NeuralDSP have their own in-house capture tech which may not be as detail orientated as the Tensorflow engine that IK have.

I'm just capturing now. Will run a fast train and then post more.
 
BTW this is the spectrum plot and analysis for an advanced ToneX capture, that I made with my D-Moll an hour ago or so.

View attachment 2035
View attachment 2036
I would just like to say thanks for sharing the captures of your nice Diezel amps on the QC Cloud ( I got them a long time ago
I just had a nice riff session on my Quad Cortex.

Happy that PC/Mac users of ToneX can get a taste of this D-Moll as well. Keep up the good work :beer
 
I would just like to say thanks for sharing the captures of your nice Diezel amps on the QC Cloud ( I got them a long time ago
I just had a nice riff session on my Quad Cortex.

Happy that PC/Mac users of ToneX can get a taste of this D-Moll as well. Keep up the good work :beer

Oh bollocks. I meant to remove those!!!



Only kidding ;)

Glad you're liking them. I did most of my amps at the time, and then flogged my Kemper coz it was a load of old phony bollocks!!

I only sold the QC coz of everything else wrong with it! :rofl
 
Haha :LOL:

But i also got 2 captures of a VH-4 from Headfirst ch 3 and ch 4 ( I think ) and they did sound a bit different from your VH-4. Must be the Loadbox i would think, or just a vh-4 mod he did maybe. Ch 4 was tighter, and not soo `loose` in the bottom
 
Haha :LOL:

But i also got 2 captures of a VH-4 from Headfirst ch 3 and ch 4 ( I think ) and they did sound a bit different from your VH-4. Must be the Loadbox i would think, or just a vh-4 mod he did maybe. Ch 4 was tighter, and not soo `loose` in the bottom

That's a nice diplomatic way of saying they were shit! :rofl

Could defo be the loadbox, I used a Suhr Reactive Load IR (without the IR portion of course), or possibly just different amp settings. Also my VH4 is from 2001, it's quite an early model. I know they did a few small changes to the circuit over the years, so it's totally possible that mine is a dark big booty haver, and his one is tighter and a bit more modern sounding??

Just goes to show though, even with the same amps, you can get different tones!
 
That's a nice diplomatic way of saying they were s**t! :rofl

Could defo be the loadbox, I used a Suhr Reactive Load IR (without the IR portion of course), or possibly just different amp settings. Also my VH4 is from 2001, it's quite an early model. I know they did a few small changes to the circuit over the years, so it's totally possible that mine is a dark big booty haver, and his one is tighter and a bit more modern sounding??

Just goes to show though, even with the same amps, you can get different tones!
No no.. I like them :hugitout

Yeah a bit more modern sounding. Yours is the hole spectrum ( as i like it) his was more just `hard/tight` But a boost on yours sound BIG
 
No no.. I like them :hugitout

Yeah a bit more modern sounding. Yours is the hole spectrum ( as i like it) his was more just `hard/tight` But a boost on yours sound BIG
My typical thing is, have the amp quite high-gain. Even to the point where it will flub out slightly. Then stick an EQ in front of it, cut some lows, and boost the highs quite dramatically. Gives me what I want without shoving me into the identikit boosted tubescreamer metal tone-zone.
 
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