compact disc playback system

[thenzeng]

Hi,
This is a assignment question:

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

I have read wikipedia and so far all I have about PCM in terms of disadvantage is that the signal accuracy for PCM is reduced because of the quantizing of the samples.

Can't find any advantages. Isn't HDCD, SACD and XRCD all improvements over the PCM technique. Which one out of the three would offer the best sonic performance?

I'll gladly appreciate any websites/comments that can help me.

THANKS,

 

[Sceadwian]

I thought the object was to compare PWM with PCM; Not PCM with HDCD, SACD, and XRCD? HDCD, SACD, and XRCD are all methods of storing/retrieving PCM data. You haven't seem to have done any study on PWM for data storage and retrieval.

 

[thenzeng]

That was part of my question

There are a lot more questions all related to the encoding/decoding scheme of compact discs.

I jumped ahead and mis-read few things in order to answer the other questions. What I meant to say was that HDCD, SACD and XRCD are all technologies aimed at offering an effective resolution of over 16-bit, with an advantage of boosting the theoretical SNR.

The second question follows on from the first about stating there advantage and disadvantages of HDCD, SACD and XRCD.

So far I have only completed reading about HDCD and partly through reading websites on SACD. So far SACD seems better, so I guess SACD would offer the best sonic performance.

Haven't read a lot about PWM am ignoring it for now and will come back to it later.

 

[Thunderchild]

well I though PCM was basically raw digitalization of analogue you get a number for every sample taken, so at each sampling you have a binary number of 8 or 16 bits per channel, for PWM it is just an on signal or and off signal and the length of the signal determines its value, these signal need to be low pass filtered to reconstruct the analogue equivalent and I suppose are easier to decode as oposed to PCM but the device outputing the PWM needs to be very fast because now in the small time between one sample and another you need to split it into 256 or 16+ million "sub sample" so that the "voltage" of that sample is represented by the time it is on or off

 

[Keruskerfuerst]

SACD has a sample frequency of 2,8224MHz and works with 1 Bit and it is not PCM based.
CD, HDCD, and DVD-Audio are PCM based with different sample frequencies up to 192kHz.

I had borrowed a Sony SACD player for one day: SACD does not sound better than CD.