Reply to post: Re: Digital Clone - billat29

How the FLAC do I tell MP3s from lossless audio?

Neil Barnes Silver badge

Re: Digital Clone - billat29

The hole in the track was part of the setup of professional (broadcast) CD players to ensure they maintained tracking across damage - there was a test CD with a series of increasingly sized holes to set up the servos. There was never any intention on a CD that the data should survive such damage, merely that you woul<tick>you woul<tick>you woul<tick>you woul<tick>you woul<tick>dn't get stuck in the 'groove'.

From memory - it's been a long time, (bloody hell, thirty years!) - the CD first tries for error recovery/correction from the parity/interleave, then tries interpolation of the signal for the duration of an error, then momentarily mutes (or holds the DC level) and only then gives up in disgust.

For what it's worth, the CD audio data is self-clocked, but uses a constant radial velocity drive to ensure the bit rate is approximately constant throughout. The bit encoding uses eight bits of thirteen (so a lot of wasted bits) to ensure sufficient transitions exist even on silence to clock the output.

Had memory been cheaper when the CD was invented, it might have been that reclocking the data - through a first in-first out memory buffer - would have been used; it would have made a noticeable difference to the audio output.

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