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Post subject: Spectral comparison of all amp models
Posted: Thu Sep 27, 2012 6:24 pm
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Aspiring Musician
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Hey guys,

I decided to try to compare the spectral signature of all Mustang amp emulations (I know is too geeky to do...) and it helped me to understand why each amp model sounds differently.

In all cases I played through the amp, a recording of an open A note (open 4th string) always at the same volume, until the note fades away (around 10 seconds play time)

The recording was made via the USB port of the amp and then analyzed via a spectrum analyzer. All graphics from 0 to 6Khz with each division meaning 748 Hz.

This first post is for the Clean Fender amps models:

57 Champ (preset 88)
Image
The most complex of the base Fender amps. A lot of harmonics that loose power very slowly.

57 Deluxe (preset 89)
Image
Strong 2nd and 3rd harmonics create the tubby sound

59 Bassman (preset 90)
Image
As you would expect very strong fundamental creates the bassy sound.

65 Princeton (preset 91)
Image
The weakest model with very weak harmonics creates a very bright and definite sound

65 Deluxe (preset 92)
Image
Similar in shape to the 57 Deluxe but with weaker higher harmoinics makes a rounder sound.

65 Twin (preset 91)
Image
Very similar to the Princeton but with a much stronger 2nd harmonic creates a much more tubby sound than the Princeton



More amps to follow later...


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 4:48 am
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Very interesting, thank you for posting this!

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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 5:19 am
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Aspiring Musician
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yes - very cool
how are you reading the 2nd / 3rd harmonics strength?
you missed the Supersonic with gain at 0!

if the fundamental is 440 hz, I can't see where that should be ?
if I'm an octave out then I should be seeing that peak at 220 hz shouldn't I??
confused..


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 6:25 am
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Professional Musician
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This is really interesting, thanks for posting.

Quote:
an open A note (open 4th string)

Hmmm, if you mean open A 5th string, then that would be 110Hz.

If you mean open D 4th string, then it would be about 147Hz. Looking at your graphs, the peaks seem to be at multiples of 147Hz so I assume the root note is open D.

Quote:
if the fundamental is 440 hz

That would be 1st string, 5th fret. (1st string = thinnest string, just in case anyone numbers them the other way round...)

NB recall that guitar music is written on a treble-clef stave "8va" - ie the written music is an octave higher than the sound.

The harmonics that are generated will depend as much on whereabouts the string is plucked, as on the amp simulation. For example, the graphs will look very different for a note plucked at its mid-point (12th fret) compared to plucked at the end. And also on what pickups are being used, and whereabouts along the string length they are.

What would be interesting would be to see the frequency response across the range with a pure sine wave. That is, inject a sine wave that 'sweeps' across the frequency range, and plot the peak amplitude for each frequency. That would show the raw modelling response curve without being coloured by the harmonics inherent in the input guitar note.

Another idea to achieve a similar result is to subtract the frequency response of the raw guitar note (ie inject the recorded guitar note directly into the spectrum analyser, then plot the difference between that graph and each of the modelled amp graphs).


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 6:35 am
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Aspiring Musician
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LOL you got that right. somebody is listening. :)
It is an open 4 string in all cases (open D)

Supersonic and all the other beasts are coming later today.

I agree injecting a pure sine wave would be interesting. In my case I wanted to "see" the effects of the amp simulation on real guitar tones. I anybody knows about a good and free spectrum analyzer I would be glad to give it a try.


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 2:29 pm
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Roadie
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scott-uk wrote:
... What would be interesting would be to see the frequency response across the range with a pure sine wave. That is, inject a sine wave that 'sweeps' across the frequency range, and plot the peak amplitude for each frequency. That would show the raw modelling response curve without being coloured by the harmonics inherent in the input guitar note.

...


This seems more useful and interesting to me.


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 3:53 pm
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Professional Musician
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Location: England
Quote:
frequency response across the range with a pure sine wave

When I get time I'll do this and post the results, but don't hold your breath, won't be imminent...

Although it dawned on me after my earlier post that it isn't that simple, there are other subtle effects at play. An amp (and thus hopefully the Mustang's amp models, if they're accurate!) will modify the input wave. The obvious example is clipping for distortion, but even without clipping the amp will change the wave in some way.

Changing the shape of a sine wave really means adding harmonics to it. So just looking at the frequency response for fundamental sine waves doesn't reflect what's really happening to the sound, and the frequency response of a guitar note won't match the simplistic sine wave frequency response I suggested earlier.

Each of the component sine waves in the input guitar note and its harmonics, will be modified by the amp, creating more harmonics that add to the input signal. The overall frequency response will be the 'basic' frequency response curve plus these additional harmonics.

Further, these additional harmonics vary in frequency with the input 'root' note - so the shape of the frequency response curve will be different for every input note. Plus, the harmonics added by the amp, and their relative amplitudes won't be the same for every input frequency, further modifying the frequency response curve...

No wonder no-one's quite developed the 'perfect' modelling amp yet!


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 8:28 pm
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Aspiring Musician
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Well, I decided to take the extra step in the name of science (!?) and do the analysis again, this time with a perfect sine wave of 247 Hz. All played at the same input level. Disregard anything below -80dB as is background noise.

This is the base sinewave
Image

Now for the Fender amps, all captures have been made using the basic presets (80s-90s)

Now first things first, so we can eliminate the controversy lets compare the Princeton and the Twin

Princeton
Image
Just a couple medium-strong harmonics and then it fades away but compared to the Twin...

Twin
Image
LOL now you know why it sounds so weak, it has pretty much NO harmonics, is almost a piano waveform. Please take note that the fundamental has the same volume as the other amps, it just sounds weaker because there are less harmonics, hence less power.

Deluxe 65
Image
This is the next in line. Similar to the Princeton but with stronger harmonics at the begining and the crucial addition of higher end harmonics that add to the tube sound (particularly even order harmonics)

Deluxe 57
Image
Even more harmonics, in this case with the particularity that harmonics 4th to 9th or so are almost at the same level which is rare and gives a distinctive ring (more metallic?) compared to the Deluxe 65

Super Sonic
Image
We see some power transfer from the fundamental to higher order harmonics as the sine wave gets more squashed

Champ
Image
The most powerful Fender signal. Not only the fundamental is among the strongest but the harmonics go on forever!


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Post subject: Re: Spectral comparison of all amp models
Posted: Fri Sep 28, 2012 9:00 pm
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Roadie
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Excellent work!

I am anxiously looking forward to more data...do you take requests? :D

Meanwhile, I need to take a closer listen to some amp models...be back later...

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Post subject: Re: Spectral comparison of all amp models
Posted: Sat Sep 29, 2012 9:19 am
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Aspiring Musician
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Thanks!
Sure I take requests.

One idea I had was to test different stomps and amp tweaks to see which one has which effect on the Twin amp to try tom improve it's reputation :)


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Post subject: Re: Spectral comparison of all amp models
Posted: Sat Sep 29, 2012 3:07 pm
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Aspiring Musician
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So i went back to my "lab" and did some more reassearch on the Twin model.
After a lot of testing a different combinations of effects I haver found and easy way to make the Twin model saturate and break in any way I want.
This is the basicv setup you need:
-dial the preset 93 , adjust only the Bias to max (+50%)

-now if you want even harmonics, just increase the amp gain, go from 4 up to 10. This will give you warm sound, and at 10 gain it sounds similar to the basic 65 Deluxe and gets pretty loud

-now if you want odd harmonics, for a more raspy sound, add the Fuzz stomp in the front of the effect chain, lower the High knob of the Fuzz effect to around 2 to limit the fuzziness, and then play with the gain control from around 2.5 up to 8. This will give you harsh distortion. If you get too much background noise simply add a noise gate to the amp (the low setting should be enough).

-now play and combine the Amp gain from 4 to 10, and the Fuzz gain from 2.5 to 8 to get a great variety of sounds


I can back all my discoveries with spectrum graphics but i got lazy yo post them :)

Enjoy your Twin simulation!


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Post subject: Re: Spectral comparison of all amp models
Posted: Sun Sep 30, 2012 8:13 pm
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This is an awesome thread!
I wish you included the Vox amp model.


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Post subject: Re: Spectral comparison of all amp models
Posted: Sun Sep 30, 2012 9:05 pm
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Aspiring Musician
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Sure, I will try to do the missing amps in the upcoming days.

One thing I discovered taking a look at the actual waveforms, particularly of the cleanest fender amps (Princeton is the best example here but it apply to Twin and Deluxe to a certain extent) is that the most versatile setting to get a variety of warm overdrive tones is as follows:
-select the amp default values
-put amp gain to max, lower volume knob to 2.5 to compensate
-put bias to max
-now, if you select your SC neck pickup, and if you roll your volume from 5 to 9 (depends on your pickup) you get a huge variety of overdrive up to saturated tones, only playing with your volume knob

-for a less aggresive, naturally compressed sound put SAG to More


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Post subject: Re: Spectral comparison of all amp models
Posted: Mon Oct 01, 2012 9:50 am
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Roadie
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Great Stuff. Really.

Comment...I have been noticing the significantly different tones I can get with my guitar volume hovering around midway and punching up the amp volume/gain...and then slowly turning up the guitar to just before things start to break apart...

Request...I'm very curious to 'see' the differences beween the two Marshall models for similarly clean and driven settings...

Cheers.

_________________
1967 Epiphone Madrid EC-30
1975 Fender Stratocaster
1981 Rickenbacker 360
2002 BC Rich Bich
2007 Fender Standard Stratocaster
2012 Taylor GA3-12
2012 Squier Telecaster
2017 Les Paul Kit


"Make every song you sing your favorite tune."


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