CD audio is not good enough, CD Standard is bad quality Options

[Joseph]

Sound quality is a complex subject, and one that has been thrashed
out elsewhere time after time. Nonetheless I'll give it a bit of a
spin here, without getting all technical, in order to justify why I
think CD audio is not good enough.

When I complain about CD sound I am not doing so as some sort of
retrograde vinyl lover who can't change with the times. :-) I am
simply saying that the sound of the CD I am listening to has audible
problems and does not match what I expect the creators wanted. This
can be measured by how closely the CD replicates the master. Of
course in most cases I don't get to hear the master, so much is
guesswork. However, as a trained audio engineer I have *some* idea of
what is expected and can certainly compare CDs to the masters I
produce.

CDs improved on vinyl in many ways, notably in reduced noise floor,
phase artifacts, and crosstalk; ease of handling; and accurate
handling of low frequency stereo information. But CDs are inferior to
vinyl in frequency response and degradation characteristics. If a CD
gets a scratch you hear unlistenable white noise; if a record gets a
scratch you hear a DJ. ;-)

Going further, some may "prefer" the sound of vinyl precisely because
of the distortions it introduces. These include rounded signal peaks
and second-order harmonics, as well as the aforementioned phase
issues. All of these introduce a "warm" sound that is palatable to
many. Whether I like that sound or not, I prefer to hear what the
artist intended. If they wanted harmonics they could have used a
tube. And so on.

A bit more is in order about error correction. Most errors are
corrected by CD players, but this can produce tiny glitches of noise
that most people do not notice. I notice them. It's not that I have
better ears; once I point them out you can hear them as well. Of
course, the better the music reproduction system the more noticable
these are. (Though contrary to this, the better the CD player error
correction, the less you'll hear.) For most people with crappy
stereos it's not an issue.

I do not think that there is anything inherently wrong with digital
sound encoding, only that the 44.1KHz sampling rate and 16 bits per
sample are not good enough. Currently, studios use 96KHz and 24 (or
32) bits throughout the recording chain process, and must reduce this
down to consumer standards for replication. There's probably a good
reason why those people most highly trained in listening don't think
CD quality is good enough for recording. It's simply because their
ears tell them so.

You may be interested to know that the current CD standard was a
matter of much compromise between the American, European, and
Japanese manufacturers. I can remember reading some of the research
articles at the time (I was in university). The Japanese insisted
that 100KHz and 24-bit (if memory serves on the exact numbers) were
required for accurate reproduction. But the others argued that no-one
would hear the difference and it would reduce cost and time to market
if the lower standard was adopted. And so, unfortunately, it was.

Another big problem with many CDs is the terrible job of mastering.
Back in vinyl days you really had to know what you were doing to
adjust the master tape to the deficiencies of the medium. There were
relatively few mastering engineers, but they knew their job. Today
almost anyone thinks they can master, and so they do... badly.

So the problems with CD can be summarised as: insufficient frequency
response, insufficient resolution, poor mastering, nasty error
characteritics, and cases that break all the time. ;-)

MP3s inherit all of these except the bit about the cases.

-- robin

[KikeG]

Nyquist called for a *minimum* of 2x the frequency.

False. Nyquist said that 2x the max. frequency is enough for perfectly sampling a band-limited signal, from a mathematical point of view. There has been some debate around if you need just 2x or just over 2x, that is. 2.00001x and such would be enough. I agree with the later interpretation.

Still, sampling at a frequency just over 2x would need a perfect filter. It is true that back in real world there are no perfect filters. That is the reason why the sampling frequency is of 44.1 KHz, to have some margin and being able to reproduce up to 20 KHz with good accuracy. In practice, with today's DACs, up to 21 KHz and a little more is possible.

Many papers have
shown that the bare minimum is not sufficient. Some are even
available on the web, if you choose to go looking.

Well, cd-audio doesn't use bare minimum, as is obvious.

About phase errors: there are no phase errors in today's DACs, because they use oversampling and FIR digital filters that have just linear phase distortion. Linear phase distortion is just a time delay, or in other words, no distortion from an audible point of view.

About aliasing: this is a non-issue in practice, unless you can hear very well on the range between 21.5 KHz and 23 KHz, where there is some remaining aliasing due to the filters used commonly.

Now, just don't say you are not interested anymore in the discussion. You have pointed to some flaws is cd audio, we have rebated them from a reasoned and technical point of view. Please say where you don't agree with these explanations.

This post has been edited by KikeG: May 2 2003, 19:01