CD audio is not good enough, CD Standard is bad quality
CD audio is not good enough, CD Standard is bad quality
May 1 2003, 04:29
Group: Members (Donating)
Joined: 7-April 03
From: Sacramento, CA
Member No.: 5871
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
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.
May 2 2003, 18:35
Joined: 27-March 02
From: California, USA
Member No.: 1631
QUOTE (Joseph @ May 1 2003 - 09:54 PM)
But never mind theory. In practice there are many people who can hear the deficiencies caused by low sampling rates, usually in terms of loss of clarity in the high end.
To clarify some of these points:
The Nyquist numbers are pure theory and do not take into account
implementation. For example, Nyquist requires a perfect low-pass
filter for the digital-to-analogue conversion. Well, such a thing
does not exist! Real filters are not perfect, but rather introduce
frequency, aliasing, and phase anomolies. Though techniques like
oversampling can help, a sampling rate of 96KHz is the perfect
solution, as it puts all of these distortions above the range of
Nyquist called for a *minimum* of 2x the frequency. Many papers have
shown that the bare minimum is not sufficient. Some are even
available on the web, if you choose to go looking.
I was illustrating that the CD format can perfectly reproduce a 20kHz sinewave and all frequencies below that - the Nyquist theory holds well enough in practice. I would agree that you need a very good anti-aliasing filter during A/D conversion to prevent aliasing, but you said one is needed for D/A conversion. This is easily implemented for CD playback with a digital LPF in oversampled systems (4x is probably sufficient in practice) followed by a very simple analog LPF to filter out the ultrasonic alias. Do you have any evidence that 96k has ABX-able superiority to 44.1k for high end clarity? I have not seen any of that evidence and would be interested to see it. In practice the LPF are not really a big problem with digital filters and oversampled A/D and D/A conversion, but I would agree that it would be nice to have the extra margin of 96k, the point being though that I don't agree that this makes "CD audio not good enough" as you titled the thread.
2) Noise shaping:
Sure, there are many ways to get the most out of CD. I am familiar with POW-R dithering, etc. I'd rather a format that does not require all of this finagling but rather delivers bit-for-bit accurate signals. >edit< Well, there's "quite good" and then there's "indistinguishable from the master". Personally, I'd go for the latter.
The CD format does deliver bit-for-bit accurate results of its 44.1/16 signal. The point was that with noise shaping to get the most out of the format that 110dB dynamic range is not a limitation and calls the question as to whether "CD audio is not good enough." Does the medium need to be "indistinguishable from the master" to be good enough for mass distribution? I don't think that needs to be a requirement.
3) Turntable performance:
Any decent turntable can play any decently maintained vinyl record with an almost complete lack of background noise. Heck, even my mid-range Linn does a fine job.
Your words "almost complete lack of backgound noise." Just keeping things honest on the hyperbole. The Linn is a fantastic piece of equipment by the way.
4) Real world CD players:
You talk of using a low-end "Techniques" and then say *I* need a better player. Ha!
The point was that even an 18 year old "low-end" Technics player can produce a nearly perfect frequency response from 20Hz to 20kHz - real world example of CD audio being a robust, high quality medium. The other point was that if your current CD player is not capable of playing back a decent CD without errors then you should replace it becuase it is probably not working properly.
I am not too sure why you doubt my veracity. I have a degrees I could wave around but I'd rather not appeal to authority.
I doubt the claims of frequent high error rates in CD becuase that has not been my experience or observation of others' experiences in the last 20 years. Yes, please keep the degrees tucked away as they are not relevant to a lively debate and I do hope you don't beleive you are the only one on this forum with academic credentials.
The debate is indeed interesting and I am a fan of "more is better" in signal quality, but I do not agree that CD audio is not good enough. Especially when the alternative formats (SACD and DVD-A) have so many other real world issues (encryption, watermarking, analog only outputs, high prices, etc.).
Perhaps a better direction for this thread would be to ask "good enough for what?" Listening to music at a PC? While jogging? In the car? In a typical home? In an anechoic chamber? Let's not forget the ability to copy legally and make the music portable - there are sound quality, cost, portability and other real world constraints that make a medium good enough.
Was that a 1 or a 0?
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