What is a SBE?
Audio CDs hold data in minimum block ("sector") sizes of 1/75th second (0.01333 seconds / 2352 bytes of data / 588 stereo samples). If you try to burn an audio file to an audio CD, and its length is not an exact number of sectors, the last sector will usually be padded with digital silence (zeros). This gap is referred to as a "sector boundary error" because it is an error caused by a large audio file having been split into individual tracks at places other than sector boundaries (1/75th second intervals).
As such, an SBE is a silence of less-than-but-not-equal-to 1/75th second found "between" audio tracks on a CD. I say "between" because technically it is at the end of the preceeding track and has nothing to do with the one that follows. In some cases, this flaw could be completely unnoticeable, as it could be only one sample, and could fit neatly into the current flow of samples. However, more likely it will leave an audible silence, or an audible click. The click is caused when the silence interrupts a "loud" part of the waveform, i.e. one that is not close to digital silence. The waveform makes a sudden jump from a loud value to silence, and then back up again to carry on when it left off. I'll add some images in a minute for clarification.
Once you burn an audio CD with SBEs, the silences become part of the audio data - they won't disappear again if/when you extract back to your computer. An audio file extracted from a CD can never have an SBE because it's come from a CD and is as such sector-boundary-aligned.
It should be noted that "SBE" has falsely become something of a catch-all term for anything that has a short (non-two-second) silence between tracks. There was an Ozric Tentacles show seeded on STG over summer straight from the master, which had silences at the end of each track that were maybe 0.05-0.1 seconds in length. I've no idea what the taper did to achieve these, but I've seen the show on tradelists noting "quite a large SBE between each track" - there's no such thing as a "large" SBE - it's by definition less than 1/75th second in length.
If you wish to avoid creating files with SBEs, split using CDWave. For assured reliability, don't actually split the files - just save the cuesheet and burn using software that can handle cuesheets (CDRWin, newer versions of Nero etc).
Thankfully, pure SBEs don't damage the audio data in any way, they just interrupt it, so with care can can be perfectly fixed by just removing the silence. The waveforms either side of the silence should automatically line up perfectly. TAO, and especially mp3 gaps, are not so easy to remedy as small parts of the audio data can be lost in the gap generation process.
I think that's pretty much everything!
see also
http://www.cdrfaq.org and
http://www.ambfaq.cjb.netSECTOR BOUNDARY ERRORS
It's best to check your shows for "sector boundary errors" (SBEs) before uploading any files. A sector boundary error results when a wav file is not the right length to exactly fill a CD sector (= 1/75th second). Most burning programs will fill the balance of the sector with silence, sometimes creating a microgap. Some burning programs will drop the partial sector altogether. For a little more discussion of SBEs, see etree's Seeding Guidelines.
SBEs usually result from a wrong setting in an audio editor when the DAT > WAV conversion is done. For example, in Cool Edit, if it's not set to Snap To Frames, it will cut the wav anywhere, not just on a sector boundary. Tracking done using CD Wave will not create SBEs.
You can check for SBEs with shntool. See the ReadMe and Tutorial files, at that link and in the zip package, for more explanation. SBEs can also be repaired reasonably easy with shntool - it just moves a little bit of each track to fill out enough for a CD sector. But be sure to preview the repair because the tracks MUST be listed in the right track sequence to repair it properly!
And of course, the md5s will change if the SBEs are repaired. md5 summer is handy for recomputing them.
There is a nearly identical functionality in flac itself to repair SBEs. shntool can also be used to check flac files for SBEs.
You'll want to have shntool, shorten and flac in your system folder (or in a folder that is in your Path) for these commands to work from any folder. You also need cygwin1.dll, which is in the zip packages.
Here are some batch files / command lines for use with shntool, the items in brackets will vary depending on the files and the user! Whether you use a separate directory is up to you. Whether you need the "no skip" option depends primarily on whether the existing shns have seek tables or not, and whether you know how to add seek tables to any files that are missing them without reprocessing the files. (See below for info on that.) For more information on batch files, see this link.
http://forums.etree.org/viewtopic.php?t=1393&start=0&postdays=0&postorder=asc&hi...Tracking the Seed for CD
Aesthetics
You should arrange your seed into tracks in a way that gives a pleasant listening experience. "Buzzkill" careless tracking of seeds is a common complaint from listeners; a little extra thought brings a lot of happiness. If the recording came from a DAT, you'll now need to track it for audio CDs from scratch. If you're seeding from a previous CD, you can optimize the tracking at this point, if necessary. Here are some tracking tips:
Place inter-disc cuts at a quiet spot in the performance (preferably at a set break, or at a pause between songs) and not in the middle of a killer jam. This sometimes means leaving a disc only partially filled so that all the segues are together on a disc. It's more important to have the music hang together cohesively than to have totally-full CDs. Discs are relatively cheap.
Find appropriate places in the performance so that it will fit on standard 74-minute CDs. 80-minute discs are plentiful and widely available now, but not everyone uses them. If you want to keep everyone happy, try to keep the discs to 74 minutes or less. (Though at this point, this is far less an issue than it once was, especially if it means fitting a show on one less disc.)
If crowd noise or a spoken story is present between tracks, track it so the crowd noise is at the end of one tune, not at the beginning of the next. (If it's a really long story, consider tracking it as a separate track.) This way, eager listeners can skip right to the beginning of a song instead of waiting through some cheering. However, if there is a short kick-off or an introduction to a song, consider putting it at the beginning of the track. Don't cut off any musical notes at the beginning of a song, even if there's talking or intro over them.
Tracking at Sector Boundaries
Paying attention to a simple technical issue during tracking can make a noticeable difference in seed quality. Each track of a standard audio CD is composed of "sectors" or "frames" that are each 1/75 second long (also expressed as 2352 bytes or 588 samples long). If a track is properly cut on a multiple of 1/75 second, it is "sector aligned", or cut "along sector boundaries." When it is not properly cut, the last sector is like a ragged end, which CD burning software just fills in with silence. Listeners will hear a click or pop between tracks because of the music -> sub-second silence -> music transition. This is extremely annoying and easily avoidable. Here are some sector boundary tips:
To avoid sector boundary errors (SBEs), just use the right tool in the right way to do your track splits. The simplest and best tool for tracking a show is [CD Wave], for Windows. The program's sole purpose is to split .wav files into proper CD sector-aligned tracks. The interface is very simple and easy to use. CDWave does not delete your original wav file; instead, it generates a separate set of tracks. Also, you can save a cue sheet with the split points for the tracks. This allows you to generate a set of split tracks and see how you like them, and if you decide to make changes you can go back and generate a new set of tracks from the original long wav file.
Most audio editing programs (e.g., Sound Forge, Cool Edit, etc.) do not automatically cut files along sector boundaries. Either change their settings to force them to split .wav files correctly (to cut on a 1/75th second CD sector boundary), or avoid them for CD tracking.
For the Mac, there is no direct equivalent of CD Wave. Dave Mallick notes, "[SoundEdit 16] is quite capable of splitting a transferred DAT into tracks. Just set ruler units to frames, set 1 second = 75 frames, and have at it. As long as you enter a whole frame value into your selection box, you get perfect sector boundary cuts every time." This is also the case for [Felt Tip Sound Studio].
Do any editing or "mastering" before doing your track splits. Never add fades or edits to .wav files after you track them. Doing so can push them out of alignment.
An easy way of checking for sector boundary errors is by use of [shntool]'s len function. If you see a -b- flag next to the listing, that indicates a boundary error. For more discussion of how to detect and repair SBEs and seek tables using shntool and shorten (with command lines or batch files), see [this etree forums thread].
For Linux (UNIX), there is a program called [wavbreaker] that will allow tracking on correct sector boundaries.
For Unix, there are two programs called [cdrdao] and [gcdmaster] for tracking CDs. gcdmaster comes in handy because writing toc/cue files for cdrdao with a text editor, by hand, is usually slightly boring at best and frustratingly tedious at worst.
If you are reseeding, recent versions of FlacFrontend have a working "align on sector boundaries" feature which can repair improperly cut files.
SBEs will sound louder or softer depending on the CD player. They may be very loud and annoying for some listeners, even if they are not noticeable on your own system.
For an example of strong feelings on the SBE issue, and more description, see SectorBoundaryDiscussion.
http://wiki.etree.org/index.php?page=SectorBoundaryDiscussionEtreeWiki - Seeding Guidelines
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