Let me start by putting this question to you. A CD-ROM can take 650MB of data, but a CD has 72 minutes of audio. 72 minutes of uncompressed stereo 16bit 44.1KHz music is 762048000 bytes, or 726.7 megabytes. So how do they fit that on there if a CD-ROM only contains 650MB?

Simple. CD Audio is stored in an error-compensating format where as CD-ROM data is stored in an error-correcting format.

Not quite. The true capacity is around 720M, unformatted. When you apply formatting to create a structure to the disk that can be read by an OS (a CD-ROM), you end up with around 647M free space. Regardless of disk structure, you can store your data as discrete bits in a stream (giving massive bit-error rates) or as symbols within an error correction scheme in a stream (giving the same bit error rate, but a reduced number of symbol defects which can effectively be corrected to almost 100% accuracy). Hence, audio disks appear to have a relatively high capacity compared to the raw data capacity of a CD-ROM. This explains (in part) why CD-ROMs can also be cranked at higher rotational speeds to get the data back - you are not listening them, but you can also do "predictive" reads with more narrowly focussed lasers.

If you pay extra to buy "speed stabilised drive mechanics" then you have been suckered ; the drive speed could drop to zero for up to a quarter of a second (in modern audio players) without affecting the playback in the least, since the data stream from the disk drive is recognised as being unstable; as a result, it is buffered in a FIFO which feeds the data out at an accurate clock rate to the DACs. As long as the FIFO is fed, then there is no need to mute. You should be paying more for accurate, synchronised output stage clocks (aka Linn) and large FIFOs, coupled to accurate, linear, high bitcount DACs.

So while ordinarily you may not hear bit, or even two- or three-bit, errors, they still exist in the audio and therefore can affect very sensitive listening devices.

On some of the players I worked on, the lower 2 or 3 bits of output to the DAC were actually supressed after tests showed that the objective, and some subjective, listening results were made worse by the addition of this data to the output path. One of the original Philips players, the CD104, became a reference deck for many radio stations for many years, even after the introduction of supposedly superior aparatus - and this was one of the few players that had bit suppression in the output stage.

Also keep in mind that these defects will affect a CD rip - the audio is not coming off the disc in the same way as a file does.

...and here lies the problem; when you rip, you take the entire bit range off the CD as raw data before processing. This means that if you have been used to a particular reproduction standard of audio playback from a given CD drive, you will inevitably surprised by the difference in sound from a rip since the ripping software is working with different source material to your CD player in the form of extra data. You then loose some of the reconstructed spectral content in the compression, and then finally you still have to play it back through a similar reconstruction process (DAC) as the CD.

My personal experience with this process (in the form of Emma empeg and Xing software) is that I have discovered extra clarity in lyrics, and can "hear" the music better, but that I seem to have on occasions lost some definition of the stereo image. This is something I (subjectively) correct by increasing the bitrate of the MP3 or using VBR; I have switched to exclusive use of VBR for this reason, and choose to RIP pieces where stereo image and clarity (classical, for example) are important at higher rates. Not very scientific, I know, but it seems to work!

Considering that the listening environment in a car at 60 mph is not the best place to listen without dynamic range compression being applied to the music (this is assuming a noise floor that rises to give a listening dynamic of possibly only 50dB), then a discussion about the introduction of a single bit output element representing a -96dB input to the output signal is pretty irrelevant.

At home, it will be a different story, but is telling that in my case, both myself and my wife now use the empeg as the preferred music source over the CD player (through the same HiFi) because we can hear lyrics and instruments properly for the first time. Before you pile in and say "that doesn't say much for your CD player", it is one of the most expensive player units produced by Panasonic a few years back - it's now gathering dust





One of the few remaining Mk1 owners...