[linux-audio-user] cd burning w/out gaps

Malcolm Baldridge linux-audio at paypc.com
Thu Apr 29 22:26:23 EDT 2004

> There was a discussion some time ago about
> burning a CD without the automatic 2 sec gap
> between the tracks. I didn't really follow it until I needed
> to do the same thing. Sorry if I'm repeating an old posting
> but I found that cdrecord has an option,
> defpregap, that can be used in this case. Just give
> $cdrecord defpregap=0  -other-options *.wav
> and it works. The tracks are searchable,and still the mix
> goes uninteruppted. Unfortunately, the man page says
> "This option may go away in the future":(

There is a proper way to do it (the same way the "big boys" do it: prepare a
DAO track sheet and burn the CD-A in DAO mode), and a hackish way to do it:
burn TAO/SAO and set the successive track gap to 0 (actually I'd wager it's
one frame, i.e., 1/75th of a second).  

You can't do this hack for the first track (whose pre-gap cannot be
shortened), but thankfully since there's no "prior track" this doesn't
matter much.

WARNING: not all burners support very small (or zero) values for this
pre-gap.  Canonical Orange Book spec says 150 frames [2 seconds] between tracks.

You can test it properly though:

Generate a 60 seconds long audio file of a 4Khz sine wave, split it into two
30 second pieces accurate to 1/75th of a second frame boundary (if possible
use a text entry to specify the cut point), or use a command line tool to
generate the source files.  

Burn both files, each as a track with pregap=0, and then capture the
playback (via analogue sampling) from your cd player and look for a glitch
near the inter-track point. [It should be audible though.]  With normal
music, depending on the content, the glitch might be masked.

If there's a 1/75th "gap" in playback, you'll get a nicely audible phase error.

I used to get away with this on my old Yamaha CDR 100 (long may it occupy my
shelf of Honoured Dead as a device of Singular Quality)...

NOTE!  The way "real" audio CDs pull off this caper is to set the PQ bits
[welcome to subcode] accordingly to "unmute" the track.

When all else looks dark and gray, look to Quality,

A focus on Quality.

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