Question about how sustain works

[yeeshkul]

Guys how come a distorted signal (not created by a flip-flop circuit) has longer sustain than a non-distorted signal from the same primary source. Can you indulge me with simple physics please?

[ashcat_lt]

It doesn't, but since the loud portion of the attack is compressed down so that it's not much louder than the quietest parts of the sustain portion, the sustain isn't lost to your ears quite so quickly.

Unless of course you're running that signal at a moderate acoustical volume in the same room as the guitar, in which case the same action makes it easier for the sound waves to "shake" the guitar and get resonant string feedback happening.  In that case you actually will get longer sustain - practically infinite, in fact.

[FiveseveN]

Distortion is compression/limiting with a lot of make-up gain: maybe 40 dB in an overdrive and 70-ish in a distortion. Thus the quiet parts get amplified (along with noise) and the loud parts are chopped off. See Jack Orman's Boosters, Gain and Distortion.
But what do flip-flops have to do with it?

Unless of course you're running that signal at a moderate acoustical volume in the same room as the guitar, in which case the same action makes it easier for the sound waves to "shake" the guitar and get resonant string feedback happening.

We usually make a distinction between feedback and sustain. There are a number of ways to get (controlled) feedback, e.g. the e-bow, Sustainiac, a fellow member attached this kind of transducer to a headstock etc.

Coming back to the general "how sustain works" question: when you hit it, you impart energy to a string. Due to its elastic nature and the fact that it's fixed in two places, it doesn't fly off, instead it starts to oscillate. The guitar, having a finite mass, absorbs some of this energy (at some frequencies more than others). The pickup's magnetic field creates a current in the string, which has its own magnetic field which slows the string down. Friction with the air (and at the nut and saddle) also slow it down, converting some of the string's energy into heat. I don't know enough about metals but I think some energy is also lost due to the non-ideal nature of the string's springiness itself. All this goes on until there is no more energy left and the string has stopped moving, when we say it has stopped sustaining.
There are two basic ways to increase sustain:
1. Prevent the energy from being lost (by using a guitar body that's less resonant in the spectrum we're interested in, by using pickups with less powerful magnets etc.).
2. Put back some energy into the string (by hitting it again or through positive mechanical feedback, which we discussed earlier).

[Mark Hammer]

We tend to think of sustain as something that is added, when in fact it is quite the opposite: it is something removed.  So what is removed?  Contrast.  Eliminate the contrast in either tone or level between the initial attack and subsequent portions of the note's lifespan, and it sounds as if it is "sustaining".

[yeeshkul]

Thanks guys. I guess i've got it

[Keppy]

But what do flip-flops have to do with it?

Distortion circuits that rely on flip-flops to turn an input trigger into an output square wave (think Escobedo PWM) create a distorted signal, but sometimes lack the sustain of other distortions because they cut off as soon as the input signal falls below the trigger threshold. I think the OP just wanted to distinguish between these circuits and the more conventional drive circuits that other posters have already explained.

[yeeshkul]

Keppy thanks, that is exactly what i meant. I just couldn't find the right words. Guys thank you for your answers!