ejn@ihlpf.UUCP (E Northrop) (02/17/84)
#N:ihlpf:4000039:000:796 ihlpf!ejn Feb 16 20:14:00 1984 Greg Rogers mentioned in his fine article that error bursts up to 4000 bits are completely correctable and bursts up to 12,300 bits are correctable by interpolation. Some questions: 1. Do ALL CD players correct to the fullest extent made possible by the coding redundancy or do some only correct errors up to, say, 2000 bits? (After all, the manufacturers are in this for the money and skimping in this area is easily hidden from the casual buyer.) 2. What is the nature of the interpolation process and what degradation (from perfection) of the signal results? 3. The bit rate of the PCM is obviously 2 * 44.1 * 16 kbps, but what is the bit rate as the data comes off of the CD (including redundancy)? Eric Northrop AT&T Bell Laboratories Naperville, IL ihlpf!ejn
gregr@tekig1.UUCP (02/19/84)
Eric, I think I can answer two of your three questions. >> 1. Do ALL CD players correct to the fullest extent made possible by the coding redundancy or do some only correct errors up to, say, 2000 bits? Unfortunately this is the one I can't answer. However the bulk of the error correction circuit is done in a single IC within the Phillips system so I should think that most companies with custom IC capability should be able to duplicate the full correction at a fairly competitive price. I would guess that Phillips sells its IC to others that license its approach??? >> 2. What is the nature of the interpolation process and what degradation (from perfection) of the signal results? In the Phillips system the process is linear interpolation between the preceeding value and the following value. The effect is a very momentary increase in distortion. Remember also that this is a relatively rare occurance (one sample interpolation every 10 hours at a BER (bit error rate) of 1*E-4). To really get a feel for the effectiveness and complexity of this error correction and concealment system you should get a copy of the Phillips Technical Review, vol 40, #6. I think it's too technical to continue to discuss in the newsgroup. >> 3. The bit rate of the PCM is obviously 2 * 44.1 * 16 kbps, but what is the bit rate as the data comes off of the CD (including redundancy)? The actual bit rate coming off the CD is 4.32 Mbits/sec. The bit density increases in the following manner. The information is divided into frames of six 16 bit samples per channel (192 = 2 x 16 x 6 audio bits/frame). After CIRC encoding additional C&D (control and display) bits and parity bits are added which yields 264 data bits/frame. The data is then modulated by the EFM (Eight to Fourteen Modulation) I discussed before, 3 merging bits are added for each resulting 14 bit pattern, and 27 sync bits are added for each frame. This brings the total to 588 bits/frame ( [264 * {14+3} / 8] + 27 ). Hence the original audio rate of 1.41 Mbit ( 2 * 44.1 * 16 kbps ) is increased by a factor of 588/192 = 3.06. This yields 4.32 Mbits/sec. Greg Rogers
mat@hou5d.UUCP (04/05/84)
Not all players do the full error-correction song-and-dance! This month's Audio reviews a cheeeeeap player from the nation's largest retailer. Apparently they kept the price down, in part, by cutting corners on the error-correction. from Mole End Mark Terribile hou5d!mat