DCC System description discussion

Hi all, I separated this because it is not closely aligned with the original question and a super interesting subject.

This is the English draft DCC system description on archive.org.

There is one in German, it contains additional info on some ICs, otherwise, it is not likely to be useful for many as it is in German and shorter.

Off topic, but I didn’t know there were 3 audio modes: stereo, 2-channel mono, joint stereo mode (3.3)

Oh, and (3.1):
ln a DCC player and/or recorder the tape can move in both directions during recording and playback at only one specified tape speed oI 4.76 cm/sec. For high speed copying a speed of 9.52 cm/sec is defined. Either direction makes use of the upper/lower half of the tape.

Really interesting stuff.

Oh, and:
A DCC recorder may record in the analogue Compact Cassette format onto an analogue Compact Cassette, but neither a DCC cassette can be recorded in the analogue Compact Cassette format nor an analogue compact cassette can be recorded in the DCC format.

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Yup, that’s one of the many interesting things that nobody knew about. 2-channel mono would have been great for things like audio books. Too bad this was only possible with prerecorded tapes.

What I find interesting is that the tape formatting is completely independent of the audio formatting: tape bullocks, tape frames, inter-frame gaps, modulation, error correction etc. are the lower level, and from that point of view, the audio is just a 384kbps data stream. The PASC / MP1 packets can be anywhere in the stream. So even though the tape transport system may be capable of switching between record and playback at the edge of every tape frame of 64KB, the PASC packets in that stream are not aligned with the tape frames and the audio decoder will always have to resynchronize at the beginning of a new recording.

Another interesting thing is that the DCC system description describes how PASC is encoded and decoded, including the acoustic model (unless I’m mistaken) whereas the MP1 standard only describes how to decode and leaves the encoding to the implementation.

=== Jac

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This was confirmed as the difference between MP1 and PASC in a document: The difference between PASC and MPEG 1 Layer 1

It needs to be tested if that really leads to lossless copies as I think was claimed somewhere.

Technically, your encoder violates the DCC standard :stuck_out_tongue_winking_eye:, but I don’t think it matters except for these copies.