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Topic: Which drive should be preferred? (Read 1219 times) previous topic - next topic
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Which drive should be preferred?

Hello,

I have a first collection of rips made using LG GSA-4163B and GSA-4167B internal drives, that require a +667 offset correction.
Later, I moved to a different setup, and now use a LG GP57EB40 (aka GP57ES40 and GP57EW40) external drive, that requires a +6 offset correction.

As I really want the best possible rips, I began to switch my previous rips to new ones using the new drive, in order to have less audio cropped (or more exactly, replaced with silent samples) at the end of the last track.

However, I recently discovered that for historical reasons, the offsets applied by EAC/AccurateRip have a 30 samples difference from the real values. It means my "+6" drive is actually a "-24" one.

In all cases (old/new drives, 30samples/real offsets) there is no issue with the beginning of the first track: at worst, a very few too much samples are cut.

What I'm concerned about, is that the new drive is actually a "read too late" one (as its real offset correction is a negative one). Which means it reads a bit after the end of the last track. I'm concerned that the drive might output jitter at the end of the last file, which is not cut because of the "30 samples" issue, resulting in some unremoved "clicking" noise at the end. Could you please help me clarify this point? Is the "+6/-30" drive still the best one, or should I return to the "+667" drive for safety? (a bit too much silence at the end is not an issue, but a clicking noise definitely is)

Please don't answer "it doesn't matter". The rips I'm doing are very important to me, and I really have to sort this out.

Re: Which drive should be preferred?

Reply #1
dBpoweramp invented AccurateRip. Freeware rippers are allowed to use this database as well.
The ripping program calculates the MD5 and compare it to the values in the AccurateRip database. If they are equal, the rip is considered correct.
Obvious when drives do have a different offset, they will start reading at a different position and as a consequence, a different MD5 will be calculated. To avoid this, the offset correction is applied.
This simply tells the ripping program where to start with the calculation.
To the best of my knowledge, offset correction has no other function.

Quote
I'm concerned that the drive might output jitter
I'm afraid you don't understand what jitter is. Jitter is a slight variation in the duration of the time step. It is inherent to using a clock (an analog device hence never perfect) in the DA stage. It has nothing to do with the values of the samples.
TheWellTemperedComputer.com

Re: Which drive should be preferred?

Reply #2
Almost all albums for the last track have no audio in the part of the audio (last half a second, way more than 30 samples), we have one test CD which does but they are rare, and it means the disc was not mastered correctly.

Re: Which drive should be preferred?

Reply #3
I'm afraid you don't understand what jitter is.
You are right, I shouldn't have used the word "jitter", which was incorrect. I meant "random noise", being afraid that as the drive reads after the actual audio data, it would basically read "raw plastic" and produce completely random noise. But this fear was unfounded, as I'm detailing after.

Almost all albums for the last track have no audio in the part of the audio [...]
Indeed, I have done a bit of research, and learned that audio CDs have a lead-out part. References:


Therefore, with my drive handled using a "+6 samples" correction, and considering the "30 samples" issue, the end of my rips are as so:

  • Actual end of audio data
  • Then 24 samples of lead-out
  • Then 6 samples of pure silence ("0x00" bytes) added by EAC

I have analyzed my rips, and depending on the CDs, sometimes the lead-out part is not made of 0x00 bytes, sometimes the record ends with 0x00 bytes even before the lead-out part has been reached.
That being said, even if it doesn't consist of "perfect" silence (0x00 bytes), the lead-out part is expected to be perceptibly silent, that's even its purpose! And we are talking of 24 samples, i.e. 0.00054 seconds…

Overall, we can say the "+6 (actually -24)" drive is a better pick than the "+667 (actually +637)" drive, as the latter cuts 0.015 seconds of actual audio data (ok, it's supposed to be perceptibly silent at this point of the record… but still, 15 ms feels a bit too much to me).
I'm definitely switching to the "+6" drive, and happily live with the rips made using the "+667" drive that I cannot re-rip (ok… I've looked at all of them to ensure the "cut-off" at the end is not perceptible…).

Thank you all for helping me to better understand the case :)

Re: Which drive should be preferred?

Reply #4
Almost all albums for the last track have no audio in the part of the audio (last half a second, way more than 30 samples)
When you say “no audio” do you mean “samples with a value of zero” or “samples with a level below a certain threshold”?

Re: Which drive should be preferred?

Reply #5
Yes often silence is not zeros but very low close to silence, that is how they master, with a reducing volume applied

Re: Which drive should be preferred?

Reply #6
In the majority of the rips I have analyzed, the bytes are 0x00 even before the "cut-off" (i.e. silence added) made by EAC. In the remaining cases, the lead-out part (or more exactly, the very few samples I'm reading from it) seems to simply be the continuation of the "perceptibly silence" from the last track.

Thus, the lead-out part is the continuation of the last track, whether it's "perfect silence" or "perceptibly silence". There is no "breakpoint" between the end of the last track and the beginning of the lead-out part. Which is great, because it means my "+6" drive is a really good pick, as reading from the lead-out part is perfectly fine.

And of course, even "not 0x00 absolute silence" is perfectly fine, as it is way, way below any perception.

Re: Which drive should be preferred?

Reply #7
For completeness: I have also noticed a few records where the silence is absolute on the spectogram, but consists of 0xFFFFFFFF samples instead of 0x00000000 samples. I don't know how the implementation works, but as these samples result in silence, they are also fine to me.

Re: Which drive should be preferred?

Reply #8
 0xFFFFFFFF  is -1, as close to zero as 1

Re: Which drive should be preferred?

Reply #9
And I thought I was going crazy with the completeness of my file tags, adding every ISRC that was missing.  :D
I wonder what is this 'disease' that prevents us from enjoying the music now.
Sometimes I have these dreams in where all we got was the vinyl and the needle and the thing sounded great.
 ;)

Re: Which drive should be preferred?

Reply #10
And I thought I ...

I do know that any of this is not relevant to audio quality but i guess its better to be careful when you are starting out.
And so, with digital, computer was put into place, and all the IT that came with it.

Re: Which drive should be preferred?

Reply #11
Just a note: I do think the audio CD format is somewhat misunderstood at times.  The offset is not a 30 sample difference when using EAC, cue tools, dbpoweramp, etc. after it corrects for the drive offset.  It's ±0, if the disc itself was written with ±0 drive or +12 if written with +12 drive, etc but there's no way to know this 99.9% of the time with a typical audio CD unless non-null samples spill into either the lead in or lead out in a way that makes this quite obvious and the drive is capable of over reading it where it happens but that involves actual investigation work and a capable drive or set drives to figure that out.

Re: Which drive should be preferred?

Reply #12
So, once again, the short answer to the question of which drive should be preferred is the drive that rips 'accurately', if both do, then it makes no difference from a quality perspective. However, a drive may be able to rip faster than another or may be able to extract better data from damaged CDs using C2 info for instance. Slightly incorrect rips can be fixed using cuetools. However, if the errors are excessive it's better just to source an undamaged CD than try to retrieve data from badly damaged one.

Have I missed anything?
Quis custodiet ipsos custodes?  ;~)

Re: Which drive should be preferred?

Reply #13
As an aside:
I wonder why I sometimes see signals with the value 0xFFFFFFFF constant over a while. Is there any equipment that "inverts phase" in the digital domain? Or is it just a fade-out that doesn't go all the way to zero and ends up at either sixteen zeroes or sixteen ones?

Re: Which drive should be preferred?

Reply #14
And I thought I ...
I do know that any of this is not relevant to audio quality but i guess its better to be careful when you are starting out.

I agree, I agree... I would think the same. I am just amused that, in my case, I would not think of this... this deep. But one certainly can.

Re: Which drive should be preferred?

Reply #15
However, a drive may be able to rip faster than another or may be able to extract better data from damaged CDs using C2 info for instance.
Here’s something to complicate it further: one of my drives (TSSTcorp, DVD-ROM TS-H353B, D500) doesn’t report C2 errors according to EAC. But a couple of weeks ago, three of my most troublesome CDs were ripped to by that drive the point where CUEtools could repair the rips, which none of the other drives I’ve tried have been able to do.

I don’t know what EAC does with C2 errors during a burst-mode rip, but based on the results above I theorize that in some cases the “raw” bad block of data may be closer to correct than what whatever EAC is spitting out.