How does the mark space ratio effect tone?

[Mark Abbott]

I'm building a Si Fuzz Face and I have been using Multisim to have a look at how it all works. I have found that the mark space ratio is uneven due to the region the first transistor is operating in.

How does this effect tone?

BTW, if you increase the current going through the second transistor, and then adjust the value of the 100K (bias/feedback) resistor, you can alter the mark space ratio.

Look forward to hearing from you.

Yours Sincerely

Mark Abbott

[Gus]

IIRC I like a 1:4

[gez]

A square wave of 50:50 duty cycle sounds the fattest.  Any deviation from this will sound thinner, even if there's more mark than space (the ear doesn't differentiate, it's all AC as far as it is concerned).

[R.G.]

Waveforms that are symmetrical - positive half is the same shape as the negative half - will have only odd harmonics (3rd, 5th, 7th...).

Waveforms that are not symmetrical will have all harmonics in a mix that is unique for that waveshape.

The 50% duty cycle has the most fundamental energy, hence it's fuller sound. As you depart from 50%, you get more harmonics and less fundamental in the mix.

Corner sharpness can only be made by high order harmonics. It takes fast little waveforms to turn corners quickly. So the sharper the corners on the waveform, the higher the harmonics involved.

As you get to very low (or high!) duty cycle waveforms, there is almost no fundamental left. The only reason you hear the fundamental is that your ear recreates the fundamental and reinserts it before sending the signal to your brain.

[Mark Abbott]

Guys thanks for the replies. That is informative. Good to hear from you again RG, it has been a while since I've heard from you.

I would'nt have picked extra harmonic content from uneven duty cycle, I'll try tweaking it by ear and throwing it into Multisim to see how it all turns out.

Thanks again for your help

Yours Sincerely

Mark Abbott