[Paranoia] Distorted sound after grabbing

[xiphmont at xiph.org]

On Wed, Apr 16, 2008 at 10:09 AM, Bill Davidsen <davidsen at tmr.com> wrote:
> Sven Heithecker wrote:
>  > Hi List-Members,
>  >
>
>  Excuse the much delayed reply, I marked this "later" and it got MUCH later.
>
> > I do have a strange problem grabbing one CD (Night of the Proms,
>  > Vol.10/2003". After grabbing, the sound is distorted. Looking at the
>  > file using an audio editor e.g. Audacity to exclude playback
>  > problems, it seems that several samples are clipped.
>  >
>
>  It is always possible that the data on the CD really is clipped. You
>  might try reripping with cddatowav (from cdrecord) and see if the data
>  looks the same. That software uses a modified paranoia library.
>
> > I got this problem with three different ROMs (Pioneer DVD-ROM
>  > ATAPIModel DVD-115 0127, SONY DVD RW DRU-500A, and VDRW SOSW-833S
>  > VRS3 (Acer notebook)), using cdparanoia 9.8 and 10.0. No difference.
>  >
>  > Of course, normal playback using my stereo works ok.
>  >
>
>  Your equipment may be compensating in some way for the problem, the
>  chances of three readers being bad in the same way are very low.

Have you looked at the data in a waveform editor?  I doubt it has
anything to do with clipping.

One of the common CD copy control schemes works by intentionally
introducing large-magnitude errors in the coded PCM data and making
sure the ECC coding marks these samples as bad.  It is very common
that CDROM drives will do the standard redbook-specified bad-sample
interpolation when playing a disc as audio, but will not do any of the
interpolation when reading an audio disc as data (it passes back the
bad samples exactly as read).  Unfortunately, many cdrom drives either
cannot pass back the ECC data or fake the ECC data making repair at
that point impossible.

CDParanoia does not currently attempt repair from the ECC data
(because it was written before any CDROMs reliably supported this
feature).  Supporting ECC and high-power reconstruction filters has
been on the todo list for a while-- not to circumvent the copy
control, but to handle legitimately badly damaged discs.  OTOH, it
would handle the copy-control case as well.

Monty