difference between aditive and substractive synthesis

[lighthouse]

Hey I know it could sound a bit stupid at this point but I`ve never went that deep into synthesis so...

Any help...

[Tusker]

Additive is when you make up a timbre from a number of "dull" waveforms ... like sine waves. Subtractive is when you take a pretty bright waveform (typically a saw or pulse) and filter it it to the timbre you desire.

In subtractive synthesis you most usually send the waveform through a low pass filter which cuts off the upper harmonics. If you use a steep filter to cut off all the harmonics except the fundamental, you get a ... sine wave.

A very clever man called fourier proposed that any periodic wave can be broken up into component sine waves. So in an additive synthesizer, you simply stack sine waves (kinda like a B3 with all the drawbars pulled out) to make a ... saw wave.

Jerry

[ImaX]

Get a math-plotting-program (for example search for TurboPlot) and type in the following:

y(x) = sin(x) + 0,5*sin(2*x) + 0,25*sin(3*x) + 0,125*sin(4*x) + 0,0625*sin(5*x)

The result is a sawtooth - you see the system if take more additive components it will be more exactly.

[lighthouse]

Wow, thanx guys, so Let`s see if I got it.

Aditive will be if I for example use two or more oscillators with sine waves to make a sound, and substractive will be if I just take a saw wave and run it through a filter.

did i got it right?

Juan Pablo

[Tusker]

Right. Adding just two sine waves, isn't really additive synthesis though. It's just two sine waves. You don't really approach the complexity of a saw wave in additive synthesis until you've got 8 or more partials at a minimum. Some additive synths provide up to 128 partials.

When digital first began to get practical, there were some additive synths which didn't have filters. So people thought of them as different methods. These days, in most synths, you are adding something and filtering something too.

Generally additive has a lot of microscopic power, because you can define envelopes/pitch, volume, etc. separately for each partial. Subtractive doesn't give that fine control, but more powerful, dramatic timbral.... and quick results.

Jerry

[Georges]

In non-musical terms. Organizing all ingredients and putting them together to cook a cake is like additive synthesis - you have to add this or that ingredient in order to obtain a given blend. You ADD something.

Buying a ready-made cake and then cutting away what you don't want to eat is like subtractive synthesis. You SUBTRACT something.

Logically, it is harder to create your own cake rather than go to the supermarket and buy one. The same applies to additive synthesis. Quite difficult to predict a sound, you have to organize yourself better.

Moreover, do not confuse additive synthesis with FM. That's a different game.

[Cary]

do not confuse additive synthesis with FM. That's a different game.
Could you elaborate on this?
I've had FM synthesis (or at least the Yamaha DX series) explained to me quite similarly; that it was basically a mess of sine waves stacked.

[lighthouse]

Thanx a lot
Yeah , explain FM too, please :oops:


Juan Pablo

[augerinn]

http://www.geocities.com/SunsetStrip/Underground/2288/2fmsynth.htm

[Georges]

--- ABOUT ADDITIVE SYNTHESIS ---

Additive synthesis (AS for convenience) is a technique which creates sounds from bottom up, as opposed to the top down approach of subtractive synthesis. The basic component of an additive synthesis sound is a set of sine waves which are added together in order to produce a given sound. Theoretically, as any sound is decomposable into a set of sine waves, you could emulate any existing instrument using additive synthesis.

The problem is "only" the complexity to program such sounds and of course the CPU power. There are many other problems associated to additive synthesis programming:

e.g.

- the complexity of this type of synthesis often creates the problem of thin sounds, in order to program a full sound (which AS is perfectly able to produce), you need to know and program the precise overtone characteristics of a sound (therefore re-synthesizing is a process used to help out here, but that one requires a hell of processing power and still has its limits)

- real-time control is difficult because you would have to change many many parameters at the same time instead of only one, two or three or whatever (morphing is therefore a technique used to allow better real-time control)

- each wave has some noise, adding them together therefore unavoidably increases the noise level of the final sound

etc.

There are really many obstacles to deal with. Ok, undeniably, as the Kawai K5000 shows, additive synthesis can provide interesting results. BUT the learning curve is damn steep and past experience with additive synthesis may not even serve for programming new AS sounds. That can be frustrating for any sound freak.

--- ABOUT FM ---

FM is far less complex than additive synthesis (ok, still a bit more difficult to seize than subtractive synthesis though). What happens is that you use the output of one oscillator (unhearable, think of it as an INPUT/raw material) to control the frequency of another oscillator (which you can actually hear, think of the sound which comes from your audio OUTPUT). You can use sine waves for this process (i.e. one sine wave modulating another) and often this is done in such a way BUT you are not limited to sine waves - you can actually use different waveforms as well. The more complex the wave of the first oscillator (also called modulating oscillator) is, the more complex the resulting oscillator/sound (number 2).

Naturally, FM is more limited than additive synthesis, as with FM, you cannot emulate all kinds of possible sounds. However, FM is easier to learn and more predictable as for the results, unlike additive synthesis which could be compared to Russian Roulette unless you have lots of time/patience and/or the possibility to perform re-synthesis for re-use as input for additive synthesis sounds.


P.S.: The information here above is of course only a scratch of the iceberg of each of the two synthesis types. Please refer to Paul Dillen for closer information about FM or refer to the many tutorials/websites on the Net. As for AS, hmmmm, do you still want to know more ? :wink:

[lighthouse]

Oh, thanx Georges that`s what I needed, and no that`s ok I just wanted to have those terms clear in my head...., but if sometime I need more info I`ll let you know.. Thanx a lot

Juan Pablo