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Mind the Pre-Gap
9 years ago
General
Let us hearken back to the days of Compact Disc Digital Audio...
The Redbook specification had a feature that was seldom used outside of professional audio, and that was the Track Index. An index was not a sub-track but more like a bookmark of a certain time in a track. Think of it like the "&t=" URL property in YouTube videos when someone calls out a specific part of the video in their comments.
The only place I've really seen indexes used is in sound effect libraries. The advantage of using indexes in a track rather than only tracks is that CDs have a limit of 99 tracks. If you use strictly tracks in something like a sound effect library, and your sound effects are on average 10 seconds long... those 99 track would get you about 16 minutes of audio. Kinda lousy for a disc that should hold 70 to 80 minutes. Fortunately, each track can have up to 99 indexes.
You could use the tracks to classify a category, say... 1957 Chevy Corvette. And this track would contain all sorts of sound effects from a '57 Vette, with indexes. Index 1 might be the door lock, 2 the door opening, 3 the door closing, etc. You lay down 5 minutes of '57 Vette effects on a single track... that's a lot more efficient use of the space. And the indexes get you right to the sound you want, rather than having to search the whole track.
Of course in the music industry, tracks do just fine filling up 70 minutes with songs, so indexes other than the first are never used. In fact, when consumer CD players first hit the scene, they showed track and index on their display. With the lack of indexes on the vast majority of CDs, the index indicator was quietly dropped on later models and nobody missed it.
There is one special index that was used on everyday CDs and that was Index 0, also known as the "pregap". I'm sure some of you owned CDs that had silence between tracks, and during that silence the elapsed time would go negative and count down to the start of the track. That is index 0. The start of the music would be index 1 and at that point the elapsed time would count upward. The special trick with index 0 was that when CD players would seek to a new track (including track 1 at the start of playback), they would start playing at index 1. This means on a track seek (manually, programmed or shuffle), the pregap is never played. It only plays when playing linearly through a CD. And this makes sense: if you're shuffling around, you don't want to hit that two seconds of silence before a track starts, or at the end of a track before seeking to the new track.
Unfortunately, sometimes it is used badly. I know on my Lion King soundtrack, the pregap to track 2 is nearly five seconds long and includes the last few seconds of the final thunderous finish to "Circle of Life" fading away. Not an issue when playing linearly, but when shuffling... track 1 ends when the pregap to track 2 begins (because it's track 2 index 0) and the player will jump off to the next track before the fade out is fully finished. Which is somewhat irksome.
Most of the time, it's used as it was inteded: for silence spacing between tracks that otherwise wouldn't need silence when playing non-linearly. But it's also been used cleverly... on The Crystal Method's debut album "Vegas", there's a little intermezzo piece between "High Roller" and "Comin' Back". It's not really part of "High Roller" and doesn't fit with "Comin' Back"... and it is in fact in the pregap to "Comin' Back". The only reason I realized something was different was one time I was listening to the CD and during this piece, I realized the counter on the player was counting down instead of up. And when it hit zero, "Comin' Back" started. And if you think about player behavior in the previous paragraph, the only way you will ever hear this piece is if you're playing linearly through the CD. If you shuffle or use programmed play, the intermezzo ceases to exist.
Which leads to the next thing: the pregap doesn't have to have silence in it. It's an index to a track and can contain anything and be any length. And this has given rise to a sinister element: the truly hidden track. You remember the "hidden" tracks on CDs where the last track would have a song, then maybe 8 minutes of silence and then something bonus that wasn't listed on the track list? There was still a tip that something was afoot... the player would keep going after the last song.
What a number of bands have done on quite a few CDs is hide a track in the pregap to track 1. Think about it: when you start playing a CD, the player seeks to track 1, index 1. So you'll never hit it even playing a CD linearly. If you seek back to track 1 from a different track, it starts playing at track 1, index 1 so you won't find it that way. The only way to find it is to start track 1, pause the player and rewind. The counter will hit zero and then start counting an increasing negative count. But who in their right mind would do that? What would possess someone to rewind at the very start of a CD?
I learned of this phenomenon on Mono Puff's CD "Unsupervised". And there are a whole lot more out there apparently.
So how do computer players handle pregap? I suppose it depends on the player these days, since the raw data is pulled off the CD and played back by the software. I fired up "Vegas" on Banshee and the intermezzo track is put at the end of "High Roller", as if it was part of that track. Your mileage may vary, depending on the software used. And if played right out of the CD drive (as in the days of yore) all bets are off.
I am reading on-line that some CD Drives do not like track 1 pregap and will report errors when reading the track or pretend like the audio is being extracted but deliver a file of silence. I'd try it out on mine, but I don't think I have a CD with such a hidden track.
One of you is thinking, "Wait! The pregap to track 1 would be a great place to stow CD-ROM data without exposing people to those teeth-cracking frequencies on conventional audio players!" This is true, and it was used for a while. In time, the Windows DLL was changed to make reading the track 1 pregap impossible. Thoughts are this was done on purpose to steer people toward the "CD-Extra" Bluebook format.
("Teeth Cracking Frequencies" courtesy of the warning on a PSX demo disc that had both data and Redbook audio on it)
The Redbook specification had a feature that was seldom used outside of professional audio, and that was the Track Index. An index was not a sub-track but more like a bookmark of a certain time in a track. Think of it like the "&t=" URL property in YouTube videos when someone calls out a specific part of the video in their comments.
The only place I've really seen indexes used is in sound effect libraries. The advantage of using indexes in a track rather than only tracks is that CDs have a limit of 99 tracks. If you use strictly tracks in something like a sound effect library, and your sound effects are on average 10 seconds long... those 99 track would get you about 16 minutes of audio. Kinda lousy for a disc that should hold 70 to 80 minutes. Fortunately, each track can have up to 99 indexes.
You could use the tracks to classify a category, say... 1957 Chevy Corvette. And this track would contain all sorts of sound effects from a '57 Vette, with indexes. Index 1 might be the door lock, 2 the door opening, 3 the door closing, etc. You lay down 5 minutes of '57 Vette effects on a single track... that's a lot more efficient use of the space. And the indexes get you right to the sound you want, rather than having to search the whole track.
Of course in the music industry, tracks do just fine filling up 70 minutes with songs, so indexes other than the first are never used. In fact, when consumer CD players first hit the scene, they showed track and index on their display. With the lack of indexes on the vast majority of CDs, the index indicator was quietly dropped on later models and nobody missed it.
There is one special index that was used on everyday CDs and that was Index 0, also known as the "pregap". I'm sure some of you owned CDs that had silence between tracks, and during that silence the elapsed time would go negative and count down to the start of the track. That is index 0. The start of the music would be index 1 and at that point the elapsed time would count upward. The special trick with index 0 was that when CD players would seek to a new track (including track 1 at the start of playback), they would start playing at index 1. This means on a track seek (manually, programmed or shuffle), the pregap is never played. It only plays when playing linearly through a CD. And this makes sense: if you're shuffling around, you don't want to hit that two seconds of silence before a track starts, or at the end of a track before seeking to the new track.
Unfortunately, sometimes it is used badly. I know on my Lion King soundtrack, the pregap to track 2 is nearly five seconds long and includes the last few seconds of the final thunderous finish to "Circle of Life" fading away. Not an issue when playing linearly, but when shuffling... track 1 ends when the pregap to track 2 begins (because it's track 2 index 0) and the player will jump off to the next track before the fade out is fully finished. Which is somewhat irksome.
Most of the time, it's used as it was inteded: for silence spacing between tracks that otherwise wouldn't need silence when playing non-linearly. But it's also been used cleverly... on The Crystal Method's debut album "Vegas", there's a little intermezzo piece between "High Roller" and "Comin' Back". It's not really part of "High Roller" and doesn't fit with "Comin' Back"... and it is in fact in the pregap to "Comin' Back". The only reason I realized something was different was one time I was listening to the CD and during this piece, I realized the counter on the player was counting down instead of up. And when it hit zero, "Comin' Back" started. And if you think about player behavior in the previous paragraph, the only way you will ever hear this piece is if you're playing linearly through the CD. If you shuffle or use programmed play, the intermezzo ceases to exist.
Which leads to the next thing: the pregap doesn't have to have silence in it. It's an index to a track and can contain anything and be any length. And this has given rise to a sinister element: the truly hidden track. You remember the "hidden" tracks on CDs where the last track would have a song, then maybe 8 minutes of silence and then something bonus that wasn't listed on the track list? There was still a tip that something was afoot... the player would keep going after the last song.
What a number of bands have done on quite a few CDs is hide a track in the pregap to track 1. Think about it: when you start playing a CD, the player seeks to track 1, index 1. So you'll never hit it even playing a CD linearly. If you seek back to track 1 from a different track, it starts playing at track 1, index 1 so you won't find it that way. The only way to find it is to start track 1, pause the player and rewind. The counter will hit zero and then start counting an increasing negative count. But who in their right mind would do that? What would possess someone to rewind at the very start of a CD?
I learned of this phenomenon on Mono Puff's CD "Unsupervised". And there are a whole lot more out there apparently.
So how do computer players handle pregap? I suppose it depends on the player these days, since the raw data is pulled off the CD and played back by the software. I fired up "Vegas" on Banshee and the intermezzo track is put at the end of "High Roller", as if it was part of that track. Your mileage may vary, depending on the software used. And if played right out of the CD drive (as in the days of yore) all bets are off.
I am reading on-line that some CD Drives do not like track 1 pregap and will report errors when reading the track or pretend like the audio is being extracted but deliver a file of silence. I'd try it out on mine, but I don't think I have a CD with such a hidden track.
One of you is thinking, "Wait! The pregap to track 1 would be a great place to stow CD-ROM data without exposing people to those teeth-cracking frequencies on conventional audio players!" This is true, and it was used for a while. In time, the Windows DLL was changed to make reading the track 1 pregap impossible. Thoughts are this was done on purpose to steer people toward the "CD-Extra" Bluebook format.
("Teeth Cracking Frequencies" courtesy of the warning on a PSX demo disc that had both data and Redbook audio on it)
Chiaroscuro
~chiaroscuro
Holy kazoly Unsupervised had a Pre-gap track? :O I knew about Token Back To Brooklyn, off of Factory Showroom by TMBG.
Xander_Opal
~xanderopal
Huh. That explains some annoying aspects to ripping CD to MP3, I think, where there's a bit of a fadeout or sound winding up to the next track or previous track... that you don't notice in linear playback, but when I set up a custom playlist, it hits the listener upside the head.
Mike Oldfield "Songs of Distant Earth" has a computer file stuffed on it in the pregap.
