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Originally Posted by dino
I understand NICAM stereo is a digital bit stream; the sound is compressed at a rate of 32khz / 14 bit accuracy (compared to 44khz / 16 bit accuracy for CD). The raw broadcast data is fed into NICAM encoders at the broadcast end and is decoded at the TV end. I think NICAM compression is lossless, but stand to be corrected on that.
NTL on the other hand uses a lossy compression technique; the audio layer of MPEG-2. Not sure whether they use the same raw broadcast data, but both methods employ encoders / decoders and are digital.
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NICAM is a method developed to deliver stereo audio via an age old RF method of distribution, it uses QPSK modulation piggy backed along with the AM video and FM mono sound. Its lossless but its not really perfect, it is limited on its bit accuracy (14 bits maybe as you say) and so quantisation noise can occur.
MPEG is fundementally lossy, thats how the companies can fit in 8, 10 whatever channels into the same space previously occupied by a single analogue channel. The audio ntl get for the most part are recieved from Sky/DTT and are sent out without any real processing by ntl. By that I mean the MPEG audio sent out on ntl is the same audio sent out by the broadcasters on other platforms.