Continuous Music CDs

[Musiclab]

When you want to make a CD where the music is continuous, what happens at the index 0 point? Let's say track 2 flows into track 3. index 0 and index 1 are right at the beginning of track 3. At the beginning of the CD frame. (1/75th of a second == 588 stereo samples). Let's say that the length of track 2 is not an exact multiple of 588 samples. What happens to the end of track 2?

Is the track extended with zero samples?
Is the track truncated at the last frame?
Is the track overlapped with the next track?
Is the track faded with the next track?

I can't find this answer anywhere?
Anyone?

[David Wright]

On classical CDs I always have ambience throughout, and of course some movements flow on without any silence gap. I have one continuous soundfile in most cases, and I make Index 0 and Index 1 coincide. Where there is a 'silent' gap (typically 7s) I place the Index 0/1 point 2s before the music start. Where the music flows through I place the Index 0/1 exactly on the required music start/entry. It is not particularly important if a track is exact multiple of 558 samples, this only affects the precision with which the Index 0/1 can be placed - no data is lost, as if you play continuously through this area the Index points are ignored.
It is worth mentioning that the 6 SMPTE frame (15 CD frame) offset is no longer required as the vast majority of CD players unmute within 1 CD frame, so I have this as the default offset. Some clients have in the past complained of hearing a fragment of the previous material when accessing 'attacca' movements if the 6 frame offset has been used.

[Musiclab]

Does that mean that the audio is always continuous (like shuffle mode in pt) but the index points remain on the grid and could be out by up to 1 frame?

I guess that not many people have time code cd players, or the like. But that would mean that if you skip to track 3, you'll miss the beginning of it.

Or does it round down? That way you'd always hear a bit of the previous track before the music comes in??

[DigiTechSupt]

Every track must have an index 1 however, only the first track of a CD must have an index 0 (zero).

If any track has a 0 (zero) index it is telling you that there is silence of some length between this track and the previous. To avoid this silence between tracks you must eliminate the zero index, this can be done a couple of ways.

1) Set the default item spacing to 0 seconds (it defaults to 2 seconds) BEFORE adding any items to a masterlist. The default item spacing can be found under the Setup menu in Masterlist CD. Of course, this only applies to separate audio files or regions added one at a time and not a single file that contains several songs.

2) If you have already added items to the masterlist and you don't want to start over and use the above method simply change the start time of each track to exactly the end time of the track before it. This must be done in the MLCD main window NOT the PQ subcode window. Also, to accurately do this remove any and all crossfades then change the start times and then re-apply any crossfades.

3) If a single item is added (imported) into MLCD that contains two or more songs and you have changed the "# Tracks" column to reflect that number of songs. You can go into the PQ subcode window and click on each zero index (except track one) and hit the delete key to remove them.

By the way, the zero index reguirement on the first track is a Red Book Audio Standard not a Digidesign requirement.

To answer your questions:

Is the track extended with zero samples? If there is actually a zero index between separate items (not a contiguous file with several songs) silence will be added by MLCD. Otherwise nothing is added.

Is the track truncated at the last frame? No, there is no truncating going on.

Is the track overlapped with the next track? only if a crossfade has been applied to these two items/tracks.

Is the track faded with the next track? Again, only if a crossfade has been applied to those two tracks.

I hope this helps.

Jon Connolly

[Marcus]

MLCD does NOT add silence if the 0 index is created in the PQ window - eg by option-clicking on the 'audio start' field to look for SDII markers. The index 1 is just shifted forward by the length of the 0 index and the actual audio remains unaffected.
This is handy for live albums etc. where the listener may occasionally want to program out chit-chat between songs on playback but retain the whole recording as one continuous record.

Marcus

[Musiclab]

Thanks for the input. This is all useful information, but has not answered my original question.

I want to know what happens between two tracks where the audio is meant to be continuous, but the first track has a length that is not a multiple of a CD frame (588 stereo samples).

Each track must start at the beginning of a CD frame. Therefor there is either too many or too few samples on the previous track. Something must be done so that the music can be continuous and next track start on the frame.

My theory is that the music is forced to be continuous, and the PQ codes (Track & Index points) are rounded up or down so that they are exactly on the frame (well they can't not be, can they?). Resulting in track and index points that could be up to a frame out depending on the length of the previous track.

This would be a problem with any CD Mastering software. I'm not picking on Masterlist. I simply want to know what it does.

[Marcus]

If the item is 1 long soundfile then the music (I should say audio - be it silence or whatever) MUST be continuous as there is no way you can edit it in MLCD to make it otherwise.

Then I suppose it's a question of whether you want the index to be rounded up or down.

My guess is, though, that if eg. you're setting indices by selecting SDII markers, MLCD will set the index at the NEAREST frame - so you're only ever going to be half a frame out at the most.

Then, the whole issue is clouded by access offsets and different CD players' speeds of un-muting. In my experience, an offset of one frame seems to give you what you heard in MLCD, at least for fairly modern players but still, the end result is going to differ very slightly from player to player.

If you want to be really anal about it, I suppose you could just work out how many samples out you were and paste that number of samples of silence on at the start. You could also work out exactly what MLCD is doing by analysing a file in SDII with the display set to 'samples', seeing exactly where a marker is and then how that relates to the position given to an index taken from that marker in MLCD. How badly do you want to know?

Marcus

[David Wright]

The PQ coding makes no difference to the audio on the disc - if the soundfile is continuous, so will be the audio on the disc.
If your tracks are not an exact number of frames long, the there will be some inaccuracy in the PQ coding. MLCD rounds down, so you may hear a fragment of the previous material. However, 1 CD frame is about 13ms which isn't much! The traditional offset was 200ms (6 SMPTE frames) which can be much more of a problem with continuous audio. Fortunately you can reduce this to 1 CD frame and most CD players will cope fine.

[Musiclab]

Thanks for the replies. I think I understand this now, but there is still one scenario not answered. Let's look at it from another angle (not continuous):

Let's say we want exactly 1.000 seconds pause between tracks. The second track is obviously going to start on a CD frame boundary. I assume this means that you will actually get 1.000 seconds +/- 1 CD frame depending on the audio and how MLCD rounds time.

If I wind that pause time back to 0.000 seconds, I'm still left with +/- 1 CD frame depending on the audio and how MLCD rounds time.

WHAT HAPPENS???

[Marcus]

A guess -

the index will be placed at the nearest CD frame within the second item. In other words, the index point will be rounded up if the second item starts at a fraction of a frame.

I'm assuming (from experience) that there's nothing to stop the two items from being right up against each other, even though the second item doesn't start at the beginning of a frame. If this wasn't the case you definitely would hear a silence gap between the two.

If MLCD rounded down in this case, it would effectively mean that the 'number of tracks' field for item 1 had changed to 2, and the same field for item 2 had changed to 0, which I can't see happening, but as I said, this is just a guess.

Marcus