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CD audio is not good enough, CD Standard is bad quality
Joseph
post May 1 2003, 04:29
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Posts: 108
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From: Newark, CA
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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
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Joseph
post May 1 2003, 16:32
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Group: Members (Donating)
Posts: 108
Joined: 7-April 03
From: Newark, CA
Member No.: 5871



paranoos wrote:

> I have to agree completely with your statement about poor mastering
> engineers in the field. The sad part is that a lot of the time,
these
> mastering 'flaws' are completely intentional.

Indeed, extremely "loud" music is all the rage. Since the ear
typically responds to average levels, not peak levels, when judging
loudness, all the mastering engineer has to do is raise the average
level as high as possible in the available dynamic range. To do so
inevitably "introduces unnecessary amounts of clipping" as you say.
Thankfully this rarely happens to any music worth hearing in the
first place -- LOL!

> I believe that 44,100 Hz, 16 bit audio is more than adequate to
> represent music, even with very high-end equipment. Each aspect
(frequency
> and resolution) can be deemed 'sufficient' by using these
benchmarks of
> human hearing, and the nature of the recording studio.

Untrue, as I will show. This is not a matter of belief, but science.

> Generally speaking, humans can perceive frequencies around 20kHz.

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
human hearing.

> I have also heard that 16bit resolution has a noise floor lower
than that of
> a silent, empty recording studio. If this is true (sorry, I don't
have hard
> evidence) then it is proof that 16bit is more than enough.

It is not true. The range of sounds from absolutely quiet (achieved
only in an anechoic chamber) to hearing damage is 150dB. A more
reasonable range to reproduce (from a recording studio to a loud
concert) is 130dB. 16-bit recordings reproduce a dynamic range of
only 96dB, whereas 24-bit recordings reproduce 120dB. 16-bit looks
rather limiting, doesn't it?

Here's another view: in music we want to listen to (not the
overcompressed crap) the peaks are much higher than the average
volume. In order to provide room for these peaks, most of the musical
information must be restricted to about half of the available bits.
It follows that to avoid compromising the signal, we need a lot more
dynamic range than 16-bit provides.

> So, why do recording engineers use higher frequency, higher
resolution
> digital audio than the rest of us peons? Can they hear better than
us?

They are trained to hear better than us, yes.

> During the production phase, it is decided that we should raise the
volume
> of the bass guitar recording in order to give a more 'rich and
funky' sound.
>
> What is the result? Noise, noise, distortion, and more noise.

I do not follow. As long as you have sufficient dynamic range to work
in, why should raising the volume result in distortion?

BTW, a good funk sound is not achieved by raising volume, but rather
by adding a goodly amount of fast-attack compression, and a nice EQ
emphasis for the finger pop to get a nice string resonance. Or at
least that's how I'd do it. ;-) (It's also got a lot to do with the
playing, of course.)

> 24/96 is used in the
> recording studio as a buffer... the noise floor of 12 tracks
recorded in
> 24bits is still lower than 1 track in 16 bits, so it still sounds
good.

Perhaps what you are trying to say is that summing 2 signals requires
one either drop the levels 3dB to achieve the same perceived
loudness, or have 3dB dynamic range available for the increased
signal level. So certainly the more bits the better during mixing.
And yes, this is more critical than in the final mix. But it hardly
follows that fewer bits are ok for listening.

> I have heard that it is a common misconception that the louder
source sounds
> better than the quiet source, even though they are identical once
you match
> volumes.

They are not identical once you match perceived loudness, which I
think is what you are saying. The compressed signals will have very
little information above the mean, whereas the uncompressed signal
will have lots. Plus, the compressed signal will have all sorts of
clipping distortion. Just about anyone will actually prefer the
uncompressed signal, as it will sound "livelier" and more dynamic.
People like dynamics -- it provides interest and doesn't tire the
ears.

But if you match the *peaks* instead, then the compressed signal will
sound louder. And we naturally like the louder of two signals, all
other factors being equal. The louder song will jump out of the radio
and sell more copies. This is the raison d'etre of maximum
compression.

The argument for extreme compression is a simplistic one that assumes
dumb listeners, an assumption I for one am not willing to make.

> Albums released today are so loud that they are clipping CD
> audio... reaching the limit of 16bit. A 24bit medium provides a
greater
> dynamic range, and thus louder recordings.

This is by no means why there is a move to higher bit depth, since an
extremely compressed song at any bit depth will sound the same. All
the lower bits are essentially unused no matter how many of them
there are.

> And to address your thoughts on dirt and scratches on various
media... if an
> LP is dusty, you will find noticeable static noise coming out of
your
> speakers. If the records are old and warped, they will sounds
wobbly, and
> will likely skip -- as will a scratched LP. Any little imperfection
in the
> record is instantly audible.

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. Traditional comments like these about bad
vinyl quality come from people who have never heard a decent hi-fi in
the first place.

> CDs are obviously digital recordings ... to the
> CD player, that means "no matter what I read, it's supposed to be
either a 1
> or a 0" ... introduce reading noise into a digital wave, and you
still get a
> digital wave -- the player can still read the original sound
through all the
> noise, because it can assume what is supposed to be read.

Wow, this is so wrong. If I am trying to read 10010011101001 and
there is a scratch and I get 10000000000000 then how exactly am I
supposed to recover the original?

True, Red Book audio uses interpolation to add redundancy to the
signal, but a big enough scratch and all is lost.

> Granted, a heavily
> scratched CD will skip, or even refuse to play... but you can
usually have
> very visible marks on your CD and still have them play perfectly.

As an aside, you can also have invisible "marks" and have it play
badly.

> Also, imperfect error correction in CD players won't
introduce 'noise'
> into the result

Um, yes it will. It is clearly audible.

> ... at worst, it will read a 0 instead of a 1, which will result in
a
> tiny pop that lasts about 1/(16 x 44100) of a second. Your brain
cannot
> perceive this.

Not even if there are thousands of them in a row?

There are other problems with CD reproduction as well, like jitter
and single-bit distortion. The great thing about 96/24 recording is
that many of the challenges of 44/16 go away. There is no need for
dither, brick-wall filters, etc. Reproduction equipment can actually
be simpler and yet achieve sonic excellence.
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Posts in this topic
- Joseph   CD audio is not good enough   May 1 2003, 04:29
- - bryant   You're absolutely right!! Those CD cas...   May 1 2003, 04:48
- - boojum   Joseph, in general I agree with your post. But th...   May 1 2003, 04:57
- - mrosscook   Joseph, Your post argues that a lot of current CD...   May 1 2003, 05:16
- - paranoos   I have to agree completely with your statement abo...   May 1 2003, 05:18
- - floyd   QUOTE (Joseph @ Apr 30 2003 - 09:29 PM)Curren...   May 1 2003, 05:43
- - Delirium   I'm pretty sure you're, frankly, incorrect...   May 1 2003, 06:14
- - sjk   QUOTE (paranoos @ Apr 30 2003 - 08:18 PM)I ha...   May 1 2003, 06:34
- - AstralStorm   QUOTE (Delirium @ May 1 2003 - 07:14 AM)To co...   May 1 2003, 07:32
- - 2Bdecided   Whilst I'm a fan of higher sample rates (in th...   May 1 2003, 10:51
- - dev0   I agree with Paranoos here completely. If masterin...   May 1 2003, 11:01
- - Uosdwis R. Dewoh   The CD standard is often taking an unfair amount o...   May 1 2003, 12:44
- - DonP   I believe the 16/44 rates are the numbers that fel...   May 1 2003, 14:32
- - Joseph   paranoos wrote: > I have to agree completely w...   May 1 2003, 16:32
- - DigitalMan   QUOTE (Joseph @ May 1 2003 - 07:32 AM)paranoo...   May 1 2003, 18:06
- - KikeG   Well, all there issues have been discussed here fr...   May 1 2003, 20:28
- - Pio2001   Joseph wrote : QUOTE CDs are inferior to vinyl in...   May 1 2003, 21:22
- - buzzy   One of the great things about HA is that discussio...   May 1 2003, 22:33
- - Uosdwis R. Dewoh   QUOTE (Joseph @ May 1 2003 - 04:32 PM)> Al...   May 1 2003, 22:41
- - KikeG   QUOTE (Pio2001 @ May 1 2003 - 09:22 PM)What...   May 2 2003, 00:21
- - Pio2001   About audible clicks, I must say that many recordi...   May 2 2003, 01:12
- - DonP   QUOTE (Pio2001 @ May 1 2003 - 03:22 PM)Actual...   May 2 2003, 01:17
- - Joseph   DigitalMan wrote > 1) Nyquist does not require...   May 2 2003, 06:54
- - Miles   QUOTE (Joseph @ May 1 2003 - 05:29 AM)... you...   May 2 2003, 08:21
- - 2Bdecided   QUOTE (Pio2001 @ May 1 2003 - 08:22 PM)2bdeci...   May 2 2003, 10:02
- - 2Bdecided   QUOTE (Joseph @ May 2 2003 - 05:54 AM)Nyquist...   May 2 2003, 10:34
- - Pio2001   QUOTE (Joseph @ May 2 2003 - 08:54 AM)It depe...   May 2 2003, 11:41
- - mrosscook   Joseph, you end your last post by saying, QUOTE B...   May 2 2003, 16:18
- - DonP   QUOTE (Pio2001 @ May 2 2003 - 05:41 AM)That...   May 2 2003, 16:43
- - bryant   QUOTE (mrosscook @ May 2 2003 - 07:18 AM)Base...   May 2 2003, 18:34
- - DigitalMan   QUOTE (Joseph @ May 1 2003 - 09:54 PM)Joseph ...   May 2 2003, 18:35
- - KikeG   QUOTE (Joseph @ May 2 2003 - 06:54 AM)Nyquist...   May 2 2003, 18:58


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