In a thread on a forum the author claimed he could hear if a bit was read incorrectly by a CD player. He didn’t tell which one of the sixteen but lets assume the worst case: the most significant bit is wrong.
If I understand redbook audio correctly this means signal volume is doubled or halved.
One word= 1/44100 so approximately 23 µs (thanks Menno) of music.
So here we have the digital equivalent of a scratch in vinyl but can we hear a spike or a dip of 23 µs?

miscalculation: not ms, but μs

A bit, one bit, sounds like "The Princess and the Pea" to me. It's BS.

http://childhoodreading.com/Edmund_Dulac_a...nd_the_Pea.html

Paul

One bit, if it is the msb, is a full-scale click. Even though it is 23 microseconds in duration, the low-pass filtering following the D/A would stretch it out, possibly to hundreds of microseconds. I would think that this would be quite audible.

He said BIT not Byte.

Paul

1 wrong bit=1 wrong byte I presume

Well first there are two bytes per channel not one, and there is error correction, and if that doesn't work, the bits and/or bytes are averaged between the two bytes before and after.

Paul

1 wrong bit is 1 wrong sample
And yeah you can hear that as a click if it's the msb.



Hmm, ok I guess it depends here whether we talk about a bit read incorrectly from the cd, or a bit incorrect in the sample returned by the cd player. Maybe the TS should clarify this

Once again if it is misread, it will be known and corrected as above.

Paul

Also the data on the CD in not in sequence to start with, it is interlaced, and there is error correction. There is a lot of processing before it goes to the DA converter.

http://findarticles.com/p/articles/mi_m0HP..._v41/ai_9683351

Paul

I’m afraid I can’t.
Somebody claimed he could hear if the player reads a bit incorrect.

Maybe we have many different cases.
Suppose we have
0000000000000000/1000000000000000/0000000000000000
Can we hear it?
Suppose we have
1111111111111111/ 0111111111111111/1111111111111111
Can we hear it?

Suppose we have
0000000000000000/1000000000000000/0000000000000000
And the 1 detected as an error, do we get
0000000000000000/0000000000000000/0000000000000000
for output?

Unless error correction doesn't work, we get

0000000000000000/1000000000000000/0000000000000000

Paul

Paulhoff has it right.

People have a tendency to think pits and lands correspond to ones and zeros; they don't!

http://en.wikipedia.org/wiki/Cross-interle...-Solomon_coding

Aren't uncorrectable errors muted on a standalone CD player according to the Red Book standard? If so, is the muted period long enough to be audible?

Cheers, Slipstreem.

That would not be one bit and/or byte, that would be a lot more than that.

Paul

Sections of audio are silenced when there is too much missing to interpolate. I think this is beyond the type error that inspired the discussion.

Yes. I've already that particular WIKI article. What I'm suggesting is that the author of the article referred to by the OP may be mistaking a muting error for a single-bit error if he's listening to the source material on a standalone CD player.

Cheers, Slipstreem.

Agreed, Greynol. This kind of error probably falls far short of triggering muting as a last line of defence, but maybe Roseval could provide us with a link to the post he's referring to so that we can all sing from the same hymn sheet.

Data isn't stored as 1s and 0s on CDs. It is stored using different lengths of valleys, which are then interpreted in such a way as to provide a bitstream. A single pit misread will not equal a single misread bit... the error correction occurs before it gets turned into binary. does that make any sense?

edit: I'm wrong. I thought the 8-14 coding mentioned below had to do with pit lengths, not binary. My bad.

No.

There are two forms of error correction on a CD, both are digital.

The lowest level is "EFM" or eight-to-fourteen modulation". It takes each byte, and turns it into 14 bits in a fashion wherein it is possible to both correct many misreads as well as tell when a misread is uncorrectable.

Then there is an interleaving, to allow for scratches, holes, pits, etc in the CD data layer.

After that a reed-solomon code is used to error correct and error check again.

After that, if the RSC can't get it right, the player either interpolates (for a block or two) or mutes.

On most CD's there is almost nothing getting past the reed-solomon code. Usually in fact nothing at all.



A single-bit error in the DAC input is almost impossible to cause.

Usually, either everything is corrected, or a large quantity of data is missing. Such is the way of digital forward error correction schemes.

I was under the impression that EFM was used in CDs primarily because it limits the number of consecutive 1s or 0s, which can prevent clock recovery. Also, it's a DC free code, which can be important in the analogue transport of digital information. I suppose it does offer some redundency, and could be thought of as error correction.

I just did some testing in MATLAB and found that it's pretty easy to hear single bit flips down to about the 9th MSB in my (noisy) office. These errors are unlikely to occur - but do occur - inside computers an across interfaces which don't offer error correction. This isn't audiophile "slightly veiled highs and constrained bass" stuff though - it's an audible, clear click or thump.

Certain pit and land combinations/geometries are excluded, but this is not the same thing as redundancy coding.

There is no question that a single bit error can be heard, but as Woodinville is saying single bit errors aren't very likely to happen inside a CD player.

I know this is a violation of TOS #15 (Thou shall not read Audiophile threads) but here it is:
How much an incorrect bit affects the sound depends on the particular bit and the particular music. In some cases a single bit in error will be obvious, in other cases inaudible
http://www.audioasylum.com/cgi/vt.mpl?f=pcaudio&m=31127

Thanks, Roseval. I promise to keep my eyes shut whilst reading it.

Cheers, Slipstreem.

One of the posters in that thread seems to be claiming that he/she can hear the difference between different .wav file players. His ears must literally have been machined from solid gold

And, linked from that thread, this page with a quote which actually makes me feel ill:

If we talk sensitivity of our hearing only I understand there is consensus in this tread that we are able to hear a single spike of approximately 23 µs.

If I understand Cabbagerat correctly even a pattern like

0000000000000000/0000000010000000/0000000000000000
is clearly audible

So flipping a bit yield audible results or am I over simplifying?

I don't believe a single word written on the page that the "Playing the file from a deeply embedded folder..." comment comes from. None of the modifications they make to the PC hardware configuration are going to make one iota of difference unless the machine was incredibly badly configured by a total idiot in the first place and wasn't even stress-test stable. Pure BS!

Cheers, Slipstreem.

You can hear

0000000000000000/0000000000000001/0000000000000000

in suitable conditions (i.e. silence with the volume turned up).


You'll be hard pushed to hear it in real music!

Cheers,
David.

Yeah, absolutely - even (as 2Bdecided said) a much less significant bit. It sounds like a sharp click or thump, depending on the music the error is embedded in.

But, as other posters have said (most notably woodinville's post) a single bit error read from a CD doesn't cause a bit error in the output stream. Indeed, even with plenty of bit errors in the CD reading, the output stream of a CD player could be absolutely perfect. Note that this is not true of reading .wavs from a hard drive, but then hard drives have much, much lower bit error rates than the CD physical layer.

E_MY_BRAIN_HURTS: /dev/nonsense: no space on file system

I so wanna see a DBT on that. Hear, see, whatever.

ETA: If you flip the sign bit on a peak in a full-scale sine wave, you'll hear it, no problem, of course, but it's still (TOS RESPECTED) hard to get ONE bit error in a CD player.

The bottom line of it all this is that many people, audiophiles included, think that it goes straight from the CD to the DA converters, IT DOESN"T, three things are important, processing, processing, processing.

Paul

Had a good laugh. Thank you.


An uncorrectable bit on the hard drive will most certainly be audible, as the operating system would raise an error, possibly completely halting the machine.

Well, if the file system read fails, yes you'll get an error message, but if the file is corrupt, or if you for instance just hex edited the wav file, and changed the MSB of an individual sample, then the consensus seems to be that yes, a click would be audible. You could try it.

Most other posters for some reason were discussing data corruption on a redbook CD, not reading a file that contains a click.

Listening to CDs for 20 years I encountered:
CDs that ‘hang’ , player reads the same spot over and over (mostly on a first generation drive)
CDs (10 years old) that won’t play at all on any drive
1 CD when played sufficiently loud, triggered the DC protection of the poweramp.
But most of the time they simply play.

I can’t remember ever having heard a spike.
I can’t say I ever came across a passage sounding ‘unnatural’, the kind of sound which make you think this is an artefact generated by the player.
So I think my personal experience is in line with the sensus communis in this tread: the error correction does its job properly and if it fails, the effect is loud and clear.

This makes me wonder, all these special programs to make sure you do have the bit perfect rip, do they make sense?

The issue is that the corrections that are applied by a CD player or your CD drive's analog output are NOT applied to the drive's digital data out. Instead we apply software to get hopefully bit exact reproduction.

If I understand post #19 correctly, all error correction is done when reading the CD. A drive able to read redbook audio applies these error correction. As far as I could judge, all correction are done in the digital domain, non in the analogue stage.

Didn't you just contradict yourself? If there was no error concealment and all uncorrectable errors were presented as-is "loud and clear", why then you did have the feeling that the passage might have been corrupted? You just told that it's possible to tell for sure, loud and clear, when it is – without any margin of doubt.

The common sense is that a single flipped bit might be audible, as long as it's not among the two or three least significant ones, and there is no similar HF content in the given fragment. However, a single wrong bit on the data medium can be corrected by any ECC code, no matter if that's CD, DVD, or HDD. No test for audibility is needed if the data bit-identical.

Edit: It would be hard to find a CD-ROM today that does not do concealment. Recall the recomendations to use burst mode for unsalvageable CDs.

I think that's correct, with the exception of the "final line of defence" muting that can take place in Red-Book compliant CD players.

I remember buying my first standalone CD player back in 1986, a Philips CD150 (still going strong), and wanting to see just how badly abused a CD could be before the player refused to error-correct it inaudibly. I drilled a series of 5mm holes in the disc working my way from the inside to the outside edge.

Amazingly, there were no audible errors until the player got to the last few tracks near the outside edge. At the very worst, small sections of silence were inserted via a gold-plated relay mounted near the analogue stages of the player.

Whilst it might be unrealistic to expect a digital extraction method to be able to deal with such massive errors transparently, the Red-Book standard most certainly can in all but the most extreme situations.

Cheers, Slipstreem.

PS Anyone care to take a guess at how many bits were going missing three-quarters of the way out on the disc for 5mm of arc? It was transparently error-corrected at least that far.

I mentioned a couple of phenomena ( stuttering, not playing, DC ouput) I do consider 'loud and clear'. These are cases where the error corrections obvious fails.

When playing a CD there will be parts free of any damage so the player will read them without needing any error corrections.
There will be damaged parts forcing the player to apply interpolation. (or mute but this again is loud and clear)

When listening to a CD one is listening to parts read correctly and parts conjectured up by the player (interpolation). I have never been able to hear the difference between a 'true' part and a interpolated one.

Single sample errors are rare, but they occur. I've spotted some, reading damaged or protected CDs (in the later case, one read gave the correct result, and a second read outputted an isolated spike, with all sourrounding data bit for bit identical in the two cases).

They do not comply with the way CIRC should correct errors, but when a CD is very damaged, strange things occur in CD players. For example, when a block is missing (*), it seems that C1 and C2 error correction is not always applied to the result in my drive.



(*) Some Cactus DataShield protected CDs have 99-blocks sectors, which 99th block is sometimes skipped by the drive, since a sector is supposed to have only 98 blocks).

I'm not sure if this ever happens in a real-world situation. I can vividly remember a Philips demonstration on a UK TV program many years ago where a standalone CD player had been modified to allow all error-correction to be disabled. The result, even when playing back a pristine condition CD that sounded fine with error-correction enabled, sounded like a badly abused 78RPM gramophone record from the 1920's.

Cheers, Slipstreem.

The lowest error rate got in CDFreaks survey of CDR burning was around 1 low level error every 10 seconds, or maybe even one in a minute, I don't remember well.

I don't think this is true. Error correction is performed before the PCM data is constructed.

In the case of ripping programs, they ask the drive to read questionable parts over again in order to give the drive a chance to deliver good data. Ripping programs do not do error correction.

Read the first post and you'll see why.

I wanted to point out that when discussing CD, everybody here assumes a corrupted CD. Yet once a HDD is mentioned, a sector with an intentionally written bad bit is assumed. We should either compare error correction of the medium, or audibility of a 1 sample long click of variable amplitude.

I have my first CD, Van Halen, 1984, plays, all my CD's play, you should keep them out of the sun and heat.

Paul

That’s putting error correction to test!



http://en.wikipedia.org/wiki/Computer_storage_density:
Compact Disks The standard defines pits that are 0.83 micrometers long and 0.5 micrometers wide, arranged in tracks spaced 1.6 micrometers apart, offering a density of about 0.90 Gbit/in².

Tracks are spaced 1.6 µm apart
5 mm=3125 tracks hit

966367641 bits per in2=1497872 bits per mm2
A 5 mm hole (19.63 mm2) contains 29410664 bits
Looks like you have beaten MP3



Maybe I shouldn't have used them as a placemat.....

This is a set of all Beethoven's piano sonates by Kempff on Deutsche Grammophon. None of them will play any more. Probably a production error

And how well would a vinyl record work,

NOT.

Paul

All my vinyl has a hole.
Do you think we are in need of evidence that analogue media like vinyl don't have error correction?