| Author |
Message |
Radium
Guest
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 Posted:
Thu Oct 06, 2005 11:05 pm Post subject:
Questions about FM synthesis and amplitude |
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Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
It would make more sense if the carrier controlled the modulator. The
carrier can only change by frequency. The modulator can change by both
frequency *and* amplitude. It would make more sense if the FM signal
generated by the carrier would be convert to audio by the modulator and
the modulator signal would be what we would hear. But that isn't the
case.
In reality, the modulator controls the carrier.
The FM output signal is the frequency-varying carrier signal. The
carrier can only change by its frequency. The carrier cannot change by
its amplitude, thus the audio cannot change by its loudness.
It would make more sense to me, if the initial signal was a signal that
only varied by its frequency [carrier] and this initial signal
modulated the latter signal [modulator] in the following manner:
1. Depth of the change of 1st signal's frequency determined the
loudness of the 2nd signal
2. Rate of the change of the 1st signal's frequency determined the
pitch of the 2nd signal
Apparantely this is not the case in FM synthesis [it is the reverse].
This is why I'm confused.
If the carrier signal is what we hear, then all we should hear is tones
whose loudness remains constant. Right? This would obviously not
classify as music.
This is one question that has been haunting me ever since I began my
interest in FM synthesis. The rest is pretty easy. Just this part that
annoys the !#$!$#$ out of me.
Any assistance would be appreciated
Thanks,
Radium
Email: glucegen1b@excite.com
I don't use glucegen1@excite.com
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Richard Dobson
Guest
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| Posted:
Thu Oct 06, 2005 11:37 pm Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium wrote:
| Quote: | Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency.
|
What system are you playing with that triggers these questions?
In FM the modulator modulates only the frequency; there is nothing to stop you
varying the amplitude of the carrier as well if you want to (which you probably
do; but also, probably, using a separate modulation source such as an ADSR
generator). Both oscillators can be varied ad lib in both amplitude and
frequency; FM arises when the frequency of the carrier is modulated at audio
rates by the modulator. At sub-audio rates, what you get is vibrato.
Only the
| Quote: | modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
|
The output level will change if there is a volume control attached to it, and/or
an envelope generator. Absent that, the output level is that of the carrier.
Modulate the amplitude of the carrier (= AM) at sub-audio rates (with a
sinusoid) and you get tremolo; which can be very nice, but this is, by
definition, unrelated to FM.
| Quote: | It would make more sense if the carrier controlled the modulator.
|
Er, no. They would no longer be carrier and modulator then, but modulator and
carrier!
The
| Quote: | carrier can only change by frequency. The modulator can change by both
frequency *and* amplitude.
|
The amplitude of the modulator changes the range of frequency modulation of the
carrier oscillator.
<hand-waving description>
Say we have a carrier at a frequency of 1000Hz. Assume peak amplitude for all
oscillators is 1.0. Ignore the frequency of the modulator for now; that "just"
controls the spectrum of the FM output. If the amplitude of the modulator is
0.25, the frequency of the carrier will be modulated between 750Hz and 1250Hz,
at a speed determined by the frequency of the modulator oscillator.
</hand-waving description>
You can try all this out easily with free software such as Csound; much more
edifying than trying to unravel what is happening inside a DX7 or whatever.
Richard Dobson |
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Tim Wescott
Guest
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| Posted:
Fri Oct 07, 2005 12:20 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium wrote:
| Quote: | Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
|
- snip confusing stuff -
| Quote: |
Your confusion confuses me, so I'm not going to try to address it. You |
seem to have started from a simple truth and glued on a bunch of extra
confusing stuff. Let's strip things back down to essentials and start
over; here's what I know:
On modulators in general:
In very general terms a modulator changes some characteristic of an
incoming (carrier) signal by some characteristic of a desired
(modulating) signal. If it's done in a sensible way then a
_de_modulator will be able to pull out a suitable replica of the
modulating signal from the modulated signal.
On FM:
In FM the modulation takes the form of a given frequency offset for a
given voltage in the modulating signal, so (for instance) +1V on the
modulator would give you +10kHz from the carrier, +0.5V would give you
+5kHz, -0.25V would give you -2.5kHz, etc.
Then the demodulation simply becomes a problem of measuring the
frequency offset from the carrier and translating it to a voltage in a
nice, linear way.
That's it. All the rest is implementation details. Once you understand
the above ask for the rest. Does this help?
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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Gerard
Guest
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| Posted:
Fri Oct 07, 2005 12:57 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium schreef:
| Quote: | Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
|
Please do not mix up radio terminology with fm synthesis as implemented
in music synthesizers...
| Quote: | It would make more sense if the carrier controlled the modulator. The
carrier can only change by frequency. The modulator can change by both
frequency *and* amplitude. It would make more sense if the FM signal
generated by the carrier would be convert to audio by the modulator and
the modulator signal would be what we would hear. But that isn't the
case.
|
See the remark above, also for some statements made below...
| Quote: | In reality, the modulator controls the carrier.
The FM output signal is the frequency-varying carrier signal. The
carrier can only change by its frequency. The carrier cannot change by
its amplitude, thus the audio cannot change by its loudness.
It would make more sense to me, if the initial signal was a signal that
only varied by its frequency [carrier] and this initial signal
modulated the latter signal [modulator] in the following manner:
1. Depth of the change of 1st signal's frequency determined the
loudness of the 2nd signal
2. Rate of the change of the 1st signal's frequency determined the
pitch of the 2nd signal
Apparantely this is not the case in FM synthesis [it is the reverse].
This is why I'm confused.
If the carrier signal is what we hear, then all we should hear is tones
whose loudness remains constant. Right? This would obviously not
classify as music.
This is one question that has been haunting me ever since I began my
interest in FM synthesis. The rest is pretty easy. Just this part that
annoys the !#$!$#$ out of me.
Any assistance would be appreciated
Thanks,
Radium
Email: glucegen1b@excite.com
I don't use glucegen1@excite.com
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Richard Dobson
Guest
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| Posted:
Fri Oct 07, 2005 1:03 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Tim Wescott wrote:
...
| Quote: | In FM the modulation takes the form of a given frequency offset for a
given voltage in the modulating signal, so (for instance) +1V on the
modulator would give you +10kHz from the carrier, +0.5V would give you
+5kHz, -0.25V would give you -2.5kHz, etc.
Then the demodulation simply becomes a problem of measuring the
frequency offset from the carrier and translating it to a voltage in a
nice, linear way.
That's it. All the rest is implementation details. Once you understand
the above ask for the rest. Does this help?
|
He's not asking about radio-style FM, but digital sound synthesis for music
applications, where both carrier and modulator are (usually sinusoid)
oscillators in the audio range. Demodulation is not relevant here. The purpose
of FM in sound synthesis is (as originally described by John Chowning) to
achieve complex and possibly inharmonic dynamically variable tones without the
cost of additive synthesis. The canonical FM instrument is somethng like the
famous "tubular bell" patch in the Yamaha DX7. Hence in the example I gave, the
carrier frequency might be 1000Hz, and the modulator might be 200Hz or lower, or
even 2000Hz and above, or something to give inharmonic tones such as 301Hz. In
one canonical use of FM, a carrier+modulator pair can be used to create a single
formant region for singing-voice synthesis.
Richard Dobson |
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Laurence Payne
Guest
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| Posted:
Fri Oct 07, 2005 1:17 am Post subject:
Re: Questions about FM synthesis and amplitude |
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On 6 Oct 2005 11:05:49 -0700, "Radium" <glucegen1@excite.com> wrote:
| Quote: |
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
|
You've read wrong :-)
Consider a simple sine wave. It's a carrier, even though there's no
modulator. It has pitch and amplitude. Why shouldn't it? Both can
be varied.
CubaseFAQ www.laurencepayne.co.uk/CubaseFAQ.htm
"Possibly the world's least impressive web site": George Perfect |
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Tim Wescott
Guest
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| Posted:
Fri Oct 07, 2005 1:26 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Richard Dobson wrote:
| Quote: | Tim Wescott wrote:
..
In FM the modulation takes the form of a given frequency offset for a
given voltage in the modulating signal, so (for instance) +1V on the
modulator would give you +10kHz from the carrier, +0.5V would give you
+5kHz, -0.25V would give you -2.5kHz, etc.
Then the demodulation simply becomes a problem of measuring the
frequency offset from the carrier and translating it to a voltage in a
nice, linear way.
That's it. All the rest is implementation details. Once you
understand the above ask for the rest. Does this help?
He's not asking about radio-style FM, but digital sound synthesis for
music applications, where both carrier and modulator are (usually
sinusoid) oscillators in the audio range. Demodulation is not relevant
here. The purpose of FM in sound synthesis is (as originally described
by John Chowning) to achieve complex and possibly inharmonic dynamically
variable tones without the cost of additive synthesis. The canonical FM
instrument is somethng like the famous "tubular bell" patch in the
Yamaha DX7. Hence in the example I gave, the carrier frequency might be
1000Hz, and the modulator might be 200Hz or lower, or even 2000Hz and
above, or something to give inharmonic tones such as 301Hz. In one
canonical use of FM, a carrier+modulator pair can be used to create a
single formant region for singing-voice synthesis.
Richard Dobson
Ahh. Hmm. Wow. (append various other expressions of interest and |
amazement).
Well, I know exactly almost nothing about the subject then.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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Jerry Avins
Guest
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| Posted:
Fri Oct 07, 2005 2:08 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium wrote:
| Quote: | Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
|
You didn't understand what you read. (Maybe it wasn't explained well.)
There is the equivalent of a volume control.
| Quote: | It would make more sense if the carrier controlled the modulator.
|
You have no idea what you're proposing. That's like saying that it would
make more sense for the light bulb to control the switch. The modulator
modulates the carrier.
| Quote: | The
carrier can only change by frequency. The modulator can change by both
frequency *and* amplitude. It would make more sense if the FM signal
generated by the carrier would be convert to audio by the modulator and
the modulator signal would be what we would hear. But that isn't the
case.
|
You guess wrongly how something works, and then complain when it becomes
clear even to you that your guess makes no sense. Grow up! This is a
technical subject, and you can't discuss it sanely without knowing the
technical details.
| Quote: | In reality, the modulator controls the carrier.
|
In reality, the switch turns the light on and off.
| Quote: | The FM output signal is the frequency-varying carrier signal. The
carrier can only change by its frequency. The carrier cannot change by
its amplitude, thus the audio cannot change by its loudness.
|
Bullshit.
| Quote: | It would make more sense to me, if the initial signal was a signal that
only varied by its frequency [carrier] and this initial signal
modulated the latter signal [modulator] in the following manner:
|
Everything would make more sense to you if you found out how they work,
instead of deciding that you know.
...
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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rhnlogic@yahoo.com
Guest
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| Posted:
Fri Oct 07, 2005 2:30 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium wrote:
| Quote: | In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness?
|
You seem to be confusing FM synthesis and an FM synth, which are two
different things.
| Quote: | If the carrier signal is what we hear, then all we should hear is tones
whose loudness remains constant. Right? This would obviously not
classify as music.
|
Lots of music was produced by Apple II's and IBM PC's (and earlier
machines) with unfiltered 1-bit speaker outputs before the advent
of sound cards. Pretty much constant loudness.
--
rhn |
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Thomas Magma
Guest
|
| Posted:
Fri Oct 07, 2005 3:57 am Post subject:
Re: Questions about FM synthesis and amplitude |
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|
"Radium" <glucegen1@excite.com> wrote in message
news:1128621949.039266.278980@g14g2000cwa.googlegroups.com...
| Quote: | Hi:
In FM synthesis, I have read that the sound we hear is the carrier
wave. But the carrier wave can only change by its frequency. Only the
modulator can change by amplitude. So how is it that the audio output
from the FM synth can change loudness? The carrier wave is the audio
output. It is very confusing and frustrating question for me.
It would make more sense if the carrier controlled the modulator. The
carrier can only change by frequency. The modulator can change by both
frequency *and* amplitude. It would make more sense if the FM signal
generated by the carrier would be convert to audio by the modulator and
the modulator signal would be what we would hear. But that isn't the
case.
In reality, the modulator controls the carrier.
The FM output signal is the frequency-varying carrier signal. The
carrier can only change by its frequency. The carrier cannot change by
its amplitude, thus the audio cannot change by its loudness.
It would make more sense to me, if the initial signal was a signal that
only varied by its frequency [carrier] and this initial signal
modulated the latter signal [modulator] in the following manner:
1. Depth of the change of 1st signal's frequency determined the
loudness of the 2nd signal
2. Rate of the change of the 1st signal's frequency determined the
pitch of the 2nd signal
Apparantely this is not the case in FM synthesis [it is the reverse].
This is why I'm confused.
If the carrier signal is what we hear, then all we should hear is tones
whose loudness remains constant. Right? This would obviously not
classify as music.
This is one question that has been haunting me ever since I began my
interest in FM synthesis. The rest is pretty easy. Just this part that
annoys the !#$!$#$ out of me.
Any assistance would be appreciated
Thanks,
Radium
Email: glucegen1b@excite.com
I don't use glucegen1@excite.com
|
I'm assuming from this post and previous posts that you are a troll. In the
subject labeled "I'm back" you state "I ain't no troll this time!". Does
this imply that you were away at some troll reform clinic? If you are not a
troll, I sincerely apologize, but please let me know what company you work
for so I can stay away from the product.
Thomas |
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Tony Beswick
Guest
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| Posted:
Fri Oct 07, 2005 3:59 am Post subject:
Re: Questions about FM synthesis and amplitude |
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I think you've got a reasonably good grasp of FM. What you seem to be
missing is the fact that there is more to your synth than just FM.
There will be other parts of the synth that control the volume, such as
an ADSR envelope.
| Quote: | 1. Depth of the change of 1st signal's frequency determined the
loudness of the 2nd signal
2. Rate of the change of the 1st signal's frequency determined the
pitch of the 2nd signal
|
I'm from the radio FM school of thought and to me this sounds bang on if
signal 1 = carrier
signal 2 = modulating signal |
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Radium
Guest
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| Posted:
Fri Oct 07, 2005 4:30 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Tim Wescott wrote:
Sorry to say it doesn't.
Here is my understanding of FM:
1. Amplitude of the modulator determines depth of the change of
carrier's frequency.
1a. An increase in the amplitude of the modulator will increase the
depth of change of the carrier's frequency
1b. A decrease in the amplitude of the modulator will decrease the
depth of change of the carrier's frequency
2. Frequency of the modulator determines rate of the change of
carrier's frequency.
2a. An increase in the modulator's frequency will increase the rate of
change of the carrier's frequency
2b. A decrease in the modulator's frequency will decrease the rate of
change of the carrier's frequency
The modulator controls the carrier. The carrier wave is what we hear.
The amplitude of the carrier does *not* change in FM. Since we hear the
carrier wave what we hear when we listen to FM synth music, how the
#!$$^%&(# is the volume of the music change within the FM synth itself?
How does the FM synth itself change the loudness of the output? Is
there any change in the audio's loudness within the FM synth?
The audio output is the FM carrier wave. An FM carrier wave can *NOT*
change by its loudness.
Oh f--k. This insterest of mine is driving me up the wall!
Someone please lend a hand of assistance here. |
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Radium
Guest
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| Posted:
Fri Oct 07, 2005 4:38 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Jerry Avins wrote:
| Quote: | Radium wrote:
It would make more sense if the carrier controlled the modulator.
You have no idea what you're proposing. That's like saying that it would
make more sense for the light bulb to control the switch. The modulator
modulates the carrier.
|
Sorry. I explained my thoughts the wrong way.
What I was trying to say is that it would make more sense if the
modulator only varied by its frequency while the carrier varied by both
amplitude and frequency.
If the FM synth carrier [the audio output the listener hears] were to
change only by its frequency [with no change in ampitude], there the
loudness of the FM music would remain constant.
When I listen to FM music on my SB16 ISA card, I don't notice the music
being constant in its loudness. So it *would* make more the sense if
the carrier changes by both amplitude and frequency while the modulator
only changed by frequency.
But on the web pages I read. The carrier does not change by its
amplitude yet I notice the change in loudness in my FM music. It just
doesn't make sense to me.
How can a sound vary in its volume if it can't change its amplitude? |
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Jerry Avins
Guest
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| Posted:
Fri Oct 07, 2005 4:42 am Post subject:
Re: Questions about FM synthesis and amplitude |
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Radium wrote:
| Quote: | Jerry Avins wrote:
Radium wrote:
It would make more sense if the carrier controlled the modulator.
You have no idea what you're proposing. That's like saying that it would
make more sense for the light bulb to control the switch. The modulator
modulates the carrier.
Sorry. I explained my thoughts the wrong way.
What I was trying to say is that it would make more sense if the
modulator only varied by its frequency while the carrier varied by both
amplitude and frequency.
|
An amplitude modulator (usually, a multiplier) does that.
| Quote: | If the FM synth carrier [the audio output the listener hears] were to
change only by its frequency [with no change in ampitude], there the
loudness of the FM music would remain constant.
|
Go to the head of the class!
| Quote: | When I listen to FM music on my SB16 ISA card, I don't notice the music
being constant in its loudness. So it *would* make more the sense if
the carrier changes by both amplitude and frequency while the modulator
only changed by frequency.
|
And what do you conclude from that?
| Quote: | But on the web pages I read. The carrier does not change by its
amplitude yet I notice the change in loudness in my FM music. It just
doesn't make sense to me.
|
You're reading the wrong pages. Don't look for FM, look for "FM synthesis".
| Quote: | How can a sound vary in its volume if it can't change its amplitude?
|
It can't, so draw the obvious conclusion.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Radium
Guest
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| Posted:
Fri Oct 07, 2005 4:42 am Post subject:
Re: Questions about FM synthesis and amplitude |
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J Ketutsalo wrote:
| Quote: | Radium wrote:
When I listen to FM music on my SB16 ISA card, I don't notice the music
being constant in its loudness. So it *would* make more the sense if
the carrier changes by both amplitude and frequency while the modulator
only changed by frequency.
But on the web pages I read. The carrier does not change by its
amplitude yet I notice the change in loudness in my FM music. It just
doesn't make sense to me.
Was there a switch to turn off the carrier?
|
Um yes. You just stop playing the tone. Simple
| Quote: | 'Cause it gets pretty damn
annoying listening to that single FM note 24/7.
|
LOL
| Quote: | It just might be that you didn't see a full synth implementation but
only the core FM algorithm. Try googling for 'adsr envelope'.
|
Would it be correct to say the an FM synth cannot alter its volume by
itself [i.e. without ADSR or a voltage-controled amplifier]?
| Quote: | How can a sound vary in its volume if it can't change its amplitude?
Well, that is another totally unrelated story...
|
Please tell me the "story" |
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