Amplitude-Modulation Synthesis

As in synth notes, etc?

Well duh, if you knew any musical terminology (which begs why you're asking here, once again, three in a row mmm?), you'd know that vibrato is a variation in pitch (FM) and tremelo is a variation in loudness (AM). Indeed, according to Google: "A periodic change in amplitude (unlike vibrato, which is a periodic change in frequency)."

Over the long term, DC coupled FM control is generally referred to as a control voltage (CV) with pitch proportional to voltage. Likewise, DC coupled AM control sets loudness and envelope shapes (cresc., decresc., etc.).

So, yeah, really, when ARE you going to actually *use* Google yourself? Too scared of leaving your diapers?

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Radium"  wrote in message 
news:1158032600.928823.30900@b28g2000cwb.googlegroups.com...
> Hi:
>
> I know of many types of synthesis for music. I am curious about two
> types -- FM and AM.
>
> Does FM synthesis have any advantages over AM synthesis? If so, what
> are those advantages?
>
> NOTE: FM and AM synthesis are *not* to be confused with FM and AM
> radio.
>
>
> Thanks,
>
> Radium
>

I did my best trying to search about the audio quality of AM synthesis vs. FM synthesis. Google didn't give crap.

Sure I found definitions for AM and FM synthesis [and how those synthesis types work] -- which I already knew long before.

However, I didn't find any website comparing the audio quality of of AM synthesis vs. FM synthesis.

AM lets you chage the amplitude (loudness) of the tone FM lets you change the frequency (pitch).

you usually need both.

Bye. Jasen

I am not aware of any popular AM synthesis algorithms. But FM synthesis is what is used in the much-maligned Yamaha OPL2 and OPL3 synth chips in early sound cards. Note that FM synthesis is *not* like vibrato; vibrato is typically a very low frequency modulation (maybe 7 Hz or so) of the "carrier" (the tone being played). Vibrato doesn't change the underlying timbre of the tone, just makes it quiver a bit.

FM synthesis uses a modulator and carrier that are typically related by a ratio of small integers like 2:3 or such. The idea is that the carrier is so heavily modulated that the waveshape itself is changed. This effect was originally called "Chowning Modulation" after the guy who wrote it up. He found that it was very effective for creating brass sounds.

When digital synths started getting popular, this was the method of choice. I think it pretty much ruled until sampling technology came along. The beauty of FM was that really complex timbres could be produced with only a few parameters. The downside was that *nothing* about the process was intuitive; every new sound was a trial-and-error creation.

One surprising reason that FM was popular was that it was easy to do. A pure sine wave was created by walking around a circular sine table with a step size proportional to the desired output frequency. To apply FM, you just had to modulate that step size... which was *also* done by walking around the same table to get the new step. So everything was done by simple lookups. Compare that to AM, which typically required that the output of the initial table lookup be multiplied by the modulator waveform. Multiplication was really slow on early hardware, so it was avoided at all costs. I even recall a method to get AM for tremolo by looking up the same carrier twice with variable phases that could be added to create the effect, just to avoid a multiply.

Earlier analog synths used subtractive synthesis, which was a lot more intuitive in that you started with a harmonic-rich sawtooth or whatever and filtered out what you didn't want. Additive synthesis was used on a few high-end systems, where you built up the tone by adding each harmonic separately; Intuitive, but really cumbersome.

Incidentally, the FM carrier and modulator didn't have to be sine waves. I recall half-sines and a few other strange waveshapes that were apparently easy to make with the hardware of the day.

Anyway, I'm sure you could use AM in the same way as FM with small integer ratios to create new waveforms. But I suspect that it won't be as useful as FM, probably because it would tend to make a conventional harmonic series, whereas FM allows a much richer spectrum. Just a guess.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Home of DaqGen, the FREEWARE signal generator

There's a garbling here in the terminology.

In the beginning, there were analog synthesis, which might be considered subtractive synthesis, since you'd start with a waveform that often had lots of harmonics, and then you'd filter it according to the sound you wanted.

"FM synthesis" was a completely different method, using digital techniques. It was the cat's meow when it came along. Freqency modulate one oscillator with another audio frequency oscillator, and it provides a different sound. This isn't the vibrato of the analog synthesizers where a very low frequency was applied to a vco to get some vibrato. I've never paid much attention to the process, but it's well documented.

I gather a lot of sound cards may still use the method, unless they've all been superceded by wavetable synthesis (which when it came along, was considered better than FM Synthesis.

I've never seen the term "AM Synthesis".

Given that the original poster seems to be making up terms, there's little reason to bother to compare. And if he did a little reading first, then he'd be in a far better place to ask questions that could be answered (and are worth answering).

Michael

By the way, you can use my freeware DaqGen signal generator to easily experiment with AM or FM synthesis and see the resultant waveform or spectrum while you listen to the results.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Home of DaqGen, the FREEWARE signal generator