Studio Projects C1

[mcolling]

Is this similar to the fact that we like our octaves to be slightly less than an octave? Hence why lots of people tune the bottom E on a guitar wrong by comparison to an electronic tuner?

It is good to have the octaves in perfect tune. But when you are tuning guitar using harmonics you tend to try and get the harmonics into perfect tune rather than the octaves. That is, you try and get the fifth of the higher string in perfect tune with the lower string in order to get a fourth interval.

However, a fourth based on the harmonics is slightly flat to the sixth semitone of the 12 note octave, since an octave does not divide perfectly into 12. Because the guitar strings are intended to be tuned to the sixth semitone of the octave, you actually want the interval to be slightly larger than the harmonics indicate. If you tuned all of your strings so that there was no "wavering" in the harmonics, the higher strings would be flat.

This is why people tune their guitars wrong when they use harmonics.

 

[noisedude]

Hmmmm ... that makes sense. Cheers!

 

[sdelsolray]

There's a paper by Russell A. Hamm about different distortions that should be easy to find with Google. But here's my thoughts on it. I'll use an A chord as an example, since that requires the least math to understand it:

An A Major chord consists of 3 notes: A (the root), C# (the third), and E (the fifth).

This A chord will start with A=440Hz, we can build the rest of the chord from there:

A =440.00
C#=554.37
E =659.26

Ok, now imagine that someone is playing the A note and clipping it badly, so you're getting a lot of 3rd and 5th harmonic distortion. Those distortions are electronically creating and are perfect 3 and 5 time multiples of the original A note. That works out to 3x440Hz=1320Hz, and 5x440Hz=2200Hz.

But remember, we live in a "tempered" world, so the 3rd and 5th note of a "real" A chord are tuned to be pleasing to the ear. So what "real notes" happen to be near those two electronic distortion frequencies?

The octave of our "tempered" E note (the 5th of the original chord) is 1318.51Hz, clashing with our electronic distortion 3rd of 1320Hz.

The second octave of our "tempered" C# note (the 3rd of our A chord) is 2217.46Hz, a pretty fair distance from our electronic 2200Hz distortion (the fifth).

In simple terms, these electronic-generated distortion 3rd and 5th harmonic notes conflict with our tempered notes and create the "uglys" that we hear.

Even order harmonics (the second and the fourth) are simply octaves of the original notes, and just contribute to the fatness of the sound - they're in perfect tune with the originals.

Does that help explain it any better?

Thanks Harvey. That helps explain things. I've noticed (at least with string instruments like the guitar) that the relative amplitude of the harmonics is lower than the fundamental. The 2nd harmonic (e.g., the first octave generated at the 12th fret of the string) is lower in volume than the full string fundamental. The 3rd harmonic (at the 7th fret) is even lower in volume, as is the 4th harmonic (at the 5th fret), etc.

Do you know if amplitude of the electronically produced even and odd order harmonics (relative to the amplitude of the fundamental) is the same as the fundamental or does it fall off like it does with string instruments in the real world?

 

[Harvey Gerst]

Thanks Harvey. That helps explain things. I've noticed (at least with string instruments like the guitar) that the relative amplitude of the harmonics is lower than the fundamental. The 2nd harmonic (e.g., the first octave generated at the 12th fret of the string) is lower in volume than the full string fundamental. The 3rd harmonic (at the 7th fret) is even lower in volume, as is the 4th harmonic (at the 5th fret), etc.

Do you know if amplitude of the electronically produced even and odd order harmonics (relative to the amplitude of the fundamental) is the same as the fundamental or does it fall off like it does with string instruments in the real world?

Electronic distortion is a strange beast. When the signal to a tube exceeds the linear portion of the tube's amplification range, tubes tend to generate even order harmonics, generally a strong second and fourth. and yes, the levels tend to be much lower than the fundamental.

Most transistors have a lot of odd order harmonic stuff, often much higher in amplitude than the 2nd and 4th harmonics.

But transistors are a different animal entirely. When the input levels of a transistor are exceeded, it's kinda like running into a brick wall. When the input levels of a tube are exceeded, it's kinda like running into a wall of Jello.
With a tube, the distortion just keeps going up as you increase the input. With a transistor, the distortion stays low, right up to the point of clipping, then it goes up dramatically, almost straight up.

These explanations are gross generalities of course, but it does help explain a lot of what most people hear when distortion occurs. MosFET transistors, for example, tend to act more like tubes in the way they handle excess signal levels.

Whoops, I forgot to answer your question.

When you see THD (Total Harmonic Distortion) figures of maybe 5%, that means that the total of all the distortion components add up to about 5% of the fundamental signal's output.

So an amp putting out 100 Watts of a 1,000Hz note (with 5% THD) will have 5 watts of signal devoted to generating distortion products, like maybe 1.5 Watts of 2nd Harmonic Distortion (at 2,000Hz), 2 Watts of 3rd Harmonic Distortion (at 3,000Hz), 1/2 Watt of 4th Harmonic Distortion (at 4,000Hz), and 1 Watt of 5th Harmonic Distortion (at 5,000Hz). The amounts of each part of the THD distortion will change, depending on the design of the circuit.

 

[OneRoomStudios]

So that brings up an interesting idea...if you had a high quality parametric EQ that you could set a specific frequency on, couldn't you just calculate the frequency(ies) causing the problem(s) and eliminate it(them)? And if so, I'm surprised no one has created a plug-in that analyses the sound, finds any frequencies that are close but still off (the ones causing the distortion) and eliminates them. That doesn't seem like it would require all that much processing power since the calculations are relatively simple, especially compared to the types of reverb algorithms that are used today.

 

[Harvey Gerst]

So that brings up an interesting idea...if you had a high quality parametric EQ that you could set a specific frequency on, couldn't you just calculate the frequency(ies) causing the problem(s) and eliminate it(them)? And if so, I'm surprised no one has created a plug-in that analyses the sound, finds any frequencies that are close but still off (the ones causing the distortion) and eliminates them. That doesn't seem like it would require all that much processing power since the calculations are relatively simple, especially compared to the types of reverb algorithms that are used today.

If you were just dealing with one note, and if the note would hold still long enough, yes. But, consider a chord, or a symphony orchestra.

What you're suggesting is already being done; they call them "feedback eliminators". But they require the note to hold still. It's a lot harder to hit a moving target.

 

[wilkee]

But transistors are a different animal entirely. When the input levels of a transistor are exceeded, it's kinda like running into a brick wall. When the input levels of a tube are exceeded, it's kinda like running into a wall of Jello.
With a tube, the distortion just keeps going up as you increase the input. With a transistor, the distortion stays low, right up to the point of clipping, then it goes up dramatically, almost straight up.
.

I remember my first all transistor Hi-Fi amplifier that used germanium output devices and sounded crap compared to the Leak 12 watt valve amps I was used too. I then got a Quad 33/303 system that sounded slightly better but it was not untill I bought myself a Cambride Audio P110* that out went the valves for good and I have been happy with solid state ever since.

Tony

* 10 weeks wages at the time!!!

 

[TAE]

Whew!

Ask a simple question!

Thanks for giving input on this...from all the pro and cons here, I figure that it's worth the investment to give it try since ..I'm on a budget

I've found one on Craigslist that is in new condition for $125

Guess I'll find out real soon what I think of this puppy as opposed to my wonderful sm 57's which are decent for their price.

TAE

 

[crazydoc]

Electronic distortion is a strange beast...

Psychoacoustics and our perception of sound is an even stranger beast. I have a very limited understanding of it, but what I have read points to the notion that we hear sounds that aren't there, and don't hear sounds that are, so I have no clue how we can determine what the "offending frequencies" are in distorted sound or a "harsh mic". Sure, we can look at the frequency plots and other objective criteria, but these don't seem to tell us what we hear.

For instance, if you take a complex waveform of 200 Hz (say a square wave), and filter out the fundamental (200 Hz), the 2nd harmonic (400 Hz), and the 3rd harmonic (600 Hz) - that is to say, so that none of these are present in the resultant waveform - the ear will still hear the tone as 200 Hz, even though neither 200 Hz nor even its octave are present. Apparently it locks on to the difference in frequency in the remaining overtones (800, 1000, 1200, 1400 ...) - 200 Hz - and perceives that as the pitch of the tone.

I'd guess there are also differences in individuals' perceptions of the same tone, that would lead one person to perceive it as "harsh", and another as "bite", another as "presence", etc...

One man's meat is another man's poison.