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Wikipedia says "yes":

It was initially designed for radios to transmit voice by modulating one waveform's frequency with another's. This is why FM radio is called FM (frequency modulation).

-- https://en.wikipedia.org/wiki/Frequency_modulation_synthesis

But I haven't found any recording to listen on the Internet.

Another excerpt from Wikipedia:

AdLib Music Synthesizer Card (1987) used Yamaha's YM3812 sound chip which produces sound via FM synthesis.

-- https://en.wikipedia.org/wiki/Ad_Lib,_Inc.#AdLib_Music_Synthesizer_Card_(1987)

However, this card wasn't able to play voices.

So, I'm trying to understand:

  • is inability of playing voices is related to this particular ancient sound card?

or

  • is it related to FM synthesis technology in general?
  • Wikipedia doesn't say yes but it's not your fault that you think it does, that paragraph of the article is written in a confusing way. If you want to hear an example of FM as used in radio, just turn on any FM radio and tune in a station! No internet requiree. Until the last 10 years, all the sound on TV was also carried using FM. So, think of it as "synthesis of new audio signal using FM (Frequency Modulation)" vs "Transmission of existing audio signal to someplace else using FM". Two very different things, both based on FM. And the second one was invented first. – little_birdie Mar 21 at 18:37
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The way to understand this is to break down the terminology. First one to look at is "Modulation" which is the term used to describe the encoding of a "carrier" signal with another "source" signal.

In the case of "amplitude modulation", the "amplitude" of a carrier wave is "modulated" with a source signal in a transmitting circuit. The "receiving" circuit is able to "demodulate" the carrier to recover the "source" signal.

The same happens with "frequency modulation", where the "frequency" of the carrier wave is "modulated" with the source signal and the overall result is then "demodulated" to recover the source signal in the receiver.

FM is the acronym used in radio to describe the use of "Frequency Modulation".

So let us look at the use of "FM Synthesis" which is basically using similar modulation techniques to produce new sounds. Whereas in radio, you are unable to listen to the modulated carrier wave, which exists in the many Megahertz of RF frequency, with FM synthesis all the resulting sounds are all in the audible range, between 20Hz and approximately 16-18KHz, depending on hearing and age.

In order to get an FM Synthesis card to reproduce a voice, you would have to work backwards from an actual voice sound and work out how to modulate an unknown source signal in order to produce an audible voice - via FM Synthesis. Your mission, should you choose to accept it, would be to work out what the unknown source signal is and the FM Modulation parameters that are required to end up with a synthesised voice.

Voice is made up of a combination of tonal sounds and atonal/noise sounds. There are endless papers on the types of sounds that make up voice, which are too numerous to mention here, but that can be easily googled. It is definitely possible to produce both the main types of sounds using an FM synthesiser, however I would suggest it is tricky to produce them all at the same time, which would be required in this application.

You would also be advised to research the CELP codec, which by design breaks down a voice sound into its component parts and then encodes it for transmission to a similar codec which can re-constitute the voice.

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    Very thoroughly :-) – john c. j. Feb 26 at 2:22
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No it isnt't.

It would be a fools errand. FM synthesis uses one wave to modify another wave to create a more complex wave. The waveform component of the human voice is rather simple (the voice box). The complex part of human speech is the mouth which acts as a super capable filter.

To sythesise human voice, the challenge is emulating the filter (the mouth). So it doesnt really matter how you create the simple voicebox emulation, the real concern is the filtering of the waveform.

So to think we could emulate the human voice through FM waveform generation is basically barking up the wrong tree.

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