Hi,
This is a assignment question which begins below:

Compare and contrast the relative advantages and disadvantages of pulse code modulation (PCM) and pulse width modulation (PWM) used in decoding ordinary (16-bit coded) CDs

Can anyone provide me some links for further research, firstly I don't know what the terms PCM and PCW mean, so would like if someone could provide a link to me which explained them.

Any other sites to help with my assignment will be appreciated.

Thanks,

 

PCM - pulse code modulation
PWM - pulse width modulation

Top Google Hits
http://en.wikipedia.org/wiki/Pulse-code_modulation
http://en.wikipedia.org/wiki/Pulse-width_modulation

Googling before posting is considered de rigeur on the forums.

 

I had already read the wikipedia link and some websites I found on google was not very clear though, so I posted here on the forum for any other sites you could recommend.

Quoting from wikipedia

A specific example would be compact disc (CD) audio which is sampled at 44,100 Hz and quantized with 16 bits (2 bytes) which can be one of 65,536 (i.e. 2^16) possible values per sample.

Why was 16 bit chosen? Can't anything higher have been used?

THANKS

 

Frankly, I'm still trying to make sense of the original question about using PCM or PWM to "decode" CD's. The data thereon is purely digital in nature, so modulation techniques are hardly germaine. The audio is digitized by an A to D converter, and played back by the reverse. Modulation never takes place.

One can find audio A to D converters of up to 24 bits. That's one part in 16 million/bit, versus 1 in 65,536 for 16 bit audio. It's a bit hard to imagine how anybody could really hear any of those last 8 low-order bits.

 

I am giving up answer the question all I can come up with is that the disadvantage of PCM is that the signal accuracy is reduced because of the quantizing of the samples.

As for advantages I don't see what PCM has when there are more better ones out there like HDCD, SACD

 

Every bit adds 6dB to the dynamic range...(also closely related to the max S/N ratio). 16 bits give a theoretical dynamic range of 96 dB and the sample rate of 44.1kHz gives a theoretical frequency response of just under half that 44.1.
When CD's were developed that was well above anything previously available, and pretty much at the limits of the then technology. Today we are capable of much more.... but apart from studio use, why bother when no one can hear the difference.