OMChroma User ManualPredefined Classes > Frequency Modulation Synthesis > Frequency Modulation Synthesis with FM-2

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Frequency Modulation Synthesis with FM-2

Tutorial FM-2

Specific Slots

Name	Description	Default value
amp	Maximum Amplitude. Linear from >0.0 to 1000 or in dB from 0 to -∞ (see Tutorial Getting Started 02 - Amplitude and Internal Editor for more details)	-6.0
f0	NOT IN SERVICE
freq	Carrier frequency	500.0
fmod	Modulating frequency	100.0
imax	Maximum index (of freq modulation) [flt]	5
imin	Minimum index (of freq modulation) [flt]	0
aenv	Amplitude Envelope [GEN]	Instance: GEN07
ienv	Envelope for the index [GEN]	Instance: GEN07

Class description

The FM-1 Class realizes a simple Frequency Modulation Synthesis with the following controls:

The main amplitude,
The frequency of the carrier,
The frequency of the modulator,
The amplitude envelope by means of a GEN routine,
The index envelope by means of a GEN routine,
The range between (imax & imin) of the index envelope.

FM-2 versus FM-1

There are few little differences between the FM-1 and FM-2 classes.

FM-1	FM-2
The Carrier is the generating frequency (f0) multiplied by the factor n1.	The Carrier is directly given.
The Modulator is the generating frequency (f0) multiplied by the factor n2.	The Modulator is directly given.
The amplitude and index envelope are initialized by a GEN05.	The amplitude and index envelope are initialized by a GEN07.
	The slot f0 is not in service.

Patch description

These examples give the same results as the Tutorial FM-1 entering the data in a different way.

The example A & B show the meaning of the FM index: the number of the components of the side-band frequencies increase with the rising of the index.

The example C focuses on the carrier frequency with a steady sideband width (10 Hz). The sound begins rough and ends with a nice vibrato for the sake of the ratio between the modulating and the carrier frequency. At the beginning the sidebands are 10% away from the carrier (10/100 = 0.1). At the end they are 0.625% away (10/1600).

The example D focuses on the ratio between the modulating and the carrier frequency.

M/C > 0.1 -> vibrato,
M/C = integer or 1/2^n -> harmonic spectra,
M/C = floating -> inharmonic spectra.

Reminder

If imax>imin the BPF given as envelope is read forwards as usual (example A) but if imax<imin the BPF is read backwards (example B).

Try to evaluate the object with both envelopes each with a different synt.

Common Red Patches

For the red patch C#ed and Synt see Appendix A

Inside the Class

Csound Orchestra of the FM-2 Class.

instr 1

idur = p3

idurosc = 1/idur

iamp = (p4 > 0.0 ? (p4*0.001*0dbfs) : (ampdbfs (p4)))

if0 = p5 ; unused here

icar = p6 ; carrier

imod = p7 ; modulating

imax = p8

imin = p9

imindev = imin*imod

imaxdev = imax*imod

ivardev = imaxdev-imindev

iaenv = p10

ienv = p11

icarfun = 1

imodfun = 2

ieps = 0.01 ; short fadeout (avoid clicks in exp envelopes)

ken poscil iamp, idurosc, iaenv ; amplitude envelope

k1 linseg 1, idur-ieps, 1, ieps, 0 ; avoid clicks

kenv = ken * k1

ki poscil ivardev, idurosc, ienv ; dynamic modulator

kind = imindev + ki

amod poscil kind, imod, imodfun

asound poscil kenv, icar+amod, icarfun ; carrier

out asound

endin

Flow chart

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