PCM=PWM?

[Magnus Danielson]

>>>>> "R" == Rob  <cyborg0 at GlobalEyes.net> writes:

 R> Is it true that pulse code modulation is the SAME as pulse width
 R> modulation?

No.

 R> I always thought this was true, that the pulse code modulation just took
 R> a simple square wave, and by shaping the pulse very quickly was able to
 R> churn out sampled sounds..Basically, radically and quickly modulating
 R> the pulse width of an existing wave form to generate all the needed
 R> harmonics and such.

Way off... PCM is the somewhat confusing name for what usually is
called sampling (which BTW is a incorrect term, because more is really
happening).

PCM really means a form of modulation where the waveform is encoded
for every sampling pulse. The encoding is being done in a binary
system.

Sampling is really when sample the contious time waveform into a
discrete time waveform (with a Sample and Hold cursuit). This discrete
time waveform is then encoded into binary code (with a Analog to
Digital Converter cursuit). What you have in the end of this
transformation is the PCM encoded waveform. It should be noted that
due to the frequency wrapping inherent of the sampling process will
usually a frequency selection filter (usually a lowpass filter) be
used to treat the signal prior sent into the S/H.

Cheers,
Magnus