Why is it called FM synthesis?

[GreenXenon]

Hi:

Most so-called "FM synths" actually use Phase Modulation Synthesis. So
why are they still referred to as FM? Wouldn't it be more appropriate
could to call them "PM synths"?

Also, isn't the math involved in PM Synthesis significantly different
from that in FM Synthesis?

Does studying the math of FM synthesis do much good when it is
actually a PM synth you're trying to design/build?


Thanks

[William Sommerwerck]

I don't know the details, but FM and PM are essentially the same thing. Take
the derivative of the signal, apply it to a PM transmitter, and you have FM.
(Or did I get that backwards? Doesn't matter -- as Tom Lehrer said, "It's
the principle that counts.")

In fact, AM can be modeled as a form of weak FM or PM modulation. At least
one ultra-high-power AM broadcast transmitter has been built using this
principle.

[Scott Dorsey]

William Sommerwerck > wrote:
>I don't know the details, but FM and PM are essentially the same thing. Take
>the derivative of the signal, apply it to a PM transmitter, and you have FM.
>(Or did I get that backwards? Doesn't matter -- as Tom Lehrer said, "It's
>the principle that counts.")

Yes, it's just a matter of one dot on top of a variable.

>In fact, AM can be modeled as a form of weak FM or PM modulation. At least
>one ultra-high-power AM broadcast transmitter has been built using this
>principle.

I think you're thinking of PWM here.... the big AM transmitters that are
basically Class-D amps.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

>> In fact, AM can be modeled as a form of weak FM or PM modulation.
>> At least one ultra-high-power AM broadcast transmitter has been built
>> using this principle.

> I think you're thinking of PWM here... the big AM transmitters that are
> basically Class-D amps.

Perhaps, but I read about a PM transmitter that used a phase-shifting
circuit (_after_ the final) to convert the signal to AM. This eliminates the
need for a huge audio-amplifier modulator.

[Jay Kadis]

In article
>,
GreenXenon > wrote:

> Hi:
>
> Most so-called "FM synths" actually use Phase Modulation Synthesis. So
> why are they still referred to as FM? Wouldn't it be more appropriate
> could to call them "PM synths"?
>
> Also, isn't the math involved in PM Synthesis significantly different
> from that in FM Synthesis?
>
> Does studying the math of FM synthesis do much good when it is
> actually a PM synth you're trying to design/build?
>
>
> Thanks

FM synthesis was patented by John Chowning and Stanford University and
exclusively licensed to Yamaha. Phase modulation was unfortunately not
covered by the patent and eventually developed by Casio as phase
distortion synthesis. Stanford's attorneys should have done a little
more research apparently. Both techniques are now in the public domain
as I understand it.

-Jay

[Danny T]

On Aug 21, 12:27*pm, Jay Kadis > wrote:
> In article
> >,
>
> *GreenXenon > wrote:
> > Hi:
>
> > Most so-called "FM synths" actually use Phase Modulation Synthesis. So
> > why are they still referred to as FM? Wouldn't it be more appropriate
> > could to call them "PM synths"?
>
> > Also, isn't the math involved in PM Synthesis significantly different
> > from that in FM Synthesis?
>
> > Does studying the math of FM synthesis do much good when it is
> > actually a PM synth you're trying to design/build?
>
> > Thanks
>
> FM synthesis was patented by John Chowning and Stanford University and
> exclusively licensed to Yamaha. *Phase modulation was unfortunately not
> covered by the patent and eventually developed by Casio as phase
> distortion synthesis. *Stanford's attorneys should have done a little
> more research apparently. *Both techniques are now in the public domain
> as I understand it.
>
> -Jay

Holly crap they are in PD - I'm way to old!

[Arkansan Raider]

Danny T wrote:

> Holly crap they are in PD - I'm way to old!

No sir, you are properly seasoned...

---Jeff

[Danny T]

On Aug 21, 2:00*pm, Arkansan Raider > wrote:
> Danny T wrote:
> > Holly crap they are in PD - I'm way to old!
>
> No sir, you are properly seasoned...
>
> ---Jeff

Properly.... or perhaps, texmex :-)

[Arkansan Raider]

Danny T wrote:
> On Aug 21, 2:00 pm, Arkansan Raider > wrote:
>> Danny T wrote:
>>> Holly crap they are in PD - I'm way to old!
>> No sir, you are properly seasoned...
>>
>> ---Jeff
>
> Properly.... or perhaps, texmex :-)

LOL

Well you certainly spiced up *that* joke. Heh.

---Jeff

[David Light]

On Fri, 21 Aug 2009 10:27:16 -0700, Jay Kadis >
wrote:

>FM synthesis was patented by John Chowning and Stanford University and
>exclusively licensed to Yamaha. Phase modulation was unfortunately not
>covered by the patent and eventually developed by Casio as phase
>distortion synthesis. Stanford's attorneys should have done a little
>more research apparently. Both techniques are now in the public domain
>as I understand it.

As similar as PM and FM may be on paper, the Casio CZ and Yamaha DX
gear sounded completely different. I've spent some time developing
patches for both. Maybe Yamaha would have been more inclined to sue
if Casio was trying to clone the DX.

[philicorda[_7_]]

On Fri, 21 Aug 2009 22:56:44 +0000, David Light wrote:

> On Fri, 21 Aug 2009 10:27:16 -0700, Jay Kadis >
> wrote:
>
>>FM synthesis was patented by John Chowning and Stanford University and
>>exclusively licensed to Yamaha. Phase modulation was unfortunately not
>>covered by the patent and eventually developed by Casio as phase
>>distortion synthesis. Stanford's attorneys should have done a little
>>more research apparently. Both techniques are now in the public domain
>>as I understand it.
>
> As similar as PM and FM may be on paper, the Casio CZ and Yamaha DX
> gear sounded completely different. I've spent some time developing
> patches for both. Maybe Yamaha would have been more inclined to sue if
> Casio was trying to clone the DX.

One difference I found was that a low frequency or static modulator
oscillator causes a pitch change in the carrier with FM, but not with PD.
Also with PD there always seems to be more of the oscillator's
fundamental pitch present in the sound.

The PM (or 'Phase Distortion' as Casio called them) synths sound warmer
to me, and are easier to program, but are a bit more limited for extreme
sounds. To enable them to get decent 'helicopter crashing into a burning
string quartet' noises, Casio added ring mod. My VZ-10M has eight
oscillators and four ring mods per voice, and you can stack four voices
together, which adds up to a lot of chaos. :)

[Geoff]

GreenXenon wrote:
> Hi:
>
> Most so-called "FM synths" actually use Phase Modulation Synthesis. So
> why are they still referred to as FM? Wouldn't it be more appropriate
> could to call them "PM synths"?

Who told you that ? It's FM.

geoff

[nebulax]

On Aug 21, 1:27*pm, Jay Kadis > wrote:
> In article
> >,
>
> *GreenXenon > wrote:
> > Hi:
>
> > Most so-called "FM synths" actually use Phase Modulation Synthesis. So
> > why are they still referred to as FM? Wouldn't it be more appropriate
> > could to call them "PM synths"?
>
> > Also, isn't the math involved in PM Synthesis significantly different
> > from that in FM Synthesis?
>
> > Does studying the math of FM synthesis do much good when it is
> > actually a PM synth you're trying to design/build?
>
> > Thanks
>
> FM synthesis was patented by John Chowning and Stanford University and
> exclusively licensed to Yamaha. *Phase modulation was unfortunately not
> covered by the patent and eventually developed by Casio as phase
> distortion synthesis. *Stanford's attorneys should have done a little
> more research apparently. *Both techniques are now in the public domain
> as I understand it.
>
> -Jay


Does anyone still make an FM synth? I guess I'll always associate FM
sound with DX-7's and bad 80's songs, neither of which are pleasant
memories for me.

-Neb

[GreenXenon]

On Aug 21, 6:56 pm, "geoff" > wrote:
> GreenXenon wrote:
> > Hi:
>
> > Most so-called "FM synths" actually use Phase Modulation Synthesis. So
> > why are they still referred to as FM? Wouldn't it be more appropriate
> > could to call them "PM synths"?
>
> Who told you that ? It's FM.
>
> geoff

Quote from http://en.wikipedia.org/wiki/Frequency_modulation_synthesis
:

"It should be noted that the implementation commercialized by Yamaha
(US Patent 4018121 Apr 1977) is actually based on phase modulation."

Quote from http://www.midibox.org/forum/index.php/topic,11394.75.html
:

"The OPL3 (and other "frequency modulation" synths) actually use phase
modulation instead of frequency modulation. The reason is that a DC
offset (eg non-zero amplitude at 0Hz) will give a frequency shift in
FM but only a phase shift in PM. See http://www.nic.funet.fi/pub/sci/audio/misc/pm-intro
for more information."

[Jonathan[_6_]]

nebulax wrote:

> Does anyone still make an FM synth?

Native Instruments has a virtual machine which can even use the same
programs as the DX7.

-- Jon

--
-
"Coloured and animated, the concerts and spectacles are as
many invitations to discover the universes of musicians and
artists who tint with happiness our reality."

[Geoff]

GreenXenon wrote:
> "The OPL3 (and other "frequency modulation" synths) actually use phase
> modulation instead of frequency modulation. The reason is that a DC
> offset (eg non-zero amplitude at 0Hz) will give a frequency shift in
> FM but only a phase shift in PM. See
> http://www.nic.funet.fi/pub/sci/audio/misc/pm-intro for more
> information."

So a simple LFO onto an operator gives no modulation on my DX7 ?

geoff

[Geoff]

nebulax wrote:

> Does anyone still make an FM synth? I guess I'll always associate FM
> sound with DX-7's and bad 80's songs, neither of which are pleasant
> memories for me.

I have heard some pleasant DX sounds. But songs (of the 80s or whenever)
have little to do with the instruments used.

geoff

[Scott Dorsey]

geoff > wrote:
>nebulax wrote:
>
>> Does anyone still make an FM synth? I guess I'll always associate FM
>> sound with DX-7's and bad 80's songs, neither of which are pleasant
>> memories for me.
>
> I have heard some pleasant DX sounds. But songs (of the 80s or whenever)
>have little to do with the instruments used.

The songs of the 80s mostly had to do with wearing very loud leisure
suits and putting upside-down flower pots on your head.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Robert Orban[_2_]]

In article >,
says...
>
>
>>> In fact, AM can be modeled as a form of weak FM or PM modulation.
>>> At least one ultra-high-power AM broadcast transmitter has been built
>>> using this principle.
>
>> I think you're thinking of PWM here... the big AM transmitters that are
>> basically Class-D amps.
>
>Perhaps, but I read about a PM transmitter that used a phase-shifting
>circuit (_after_ the final) to convert the signal to AM. This eliminates the
>need for a huge audio-amplifier modulator.

That would be the RCA Ampliphase, which used two CW RF power amplifiers into
a combining network. The carrier phase of one side was shifted with respect
to the other side to produce AM. It was a very clever idea but it proved to
be touchy, unstable and troublesome when reduced to real hardware. When PDM
modulators came along (IIRC, the Harris/Gates MWxx series was first),
stations were very quick to dump their Ampliphase transmitters.

Bear in mind that Ampliphase was always a minority technology. The mainstream
modulation technique in the time of the Ampliphase was high-level plate
modulation using a transformer, a reactor, and a very high-powered class-B
audio amplifier that fed the transformer's primary. These transmitters were
quite inefficient compared to the best of today's tech but the best ones were
very stable and robust.

Another popular minority modulation technology at the time was Doherty (a
sophisticated form of screen modulation), used by Continental for many years.
The robustness of these transitters was competitive with high-level plate
modulation and the Continental AM transmitters using this tech were well
regarded.

Bob Orban