Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

How CD pregaps gained their hidden track superpowers

tedium.co

Post reply on HN
Print view View original

131–138 of 138 posts

Re: How CD pregaps gained their hidden track superpowers

#131

Post by qingcharles »

ssl-3 wrote: post #95
piperswe wrote: post #90

Earlier quoted context omitted.

You mentioned MKV - Matroska (MKA for audio, MKV for video) could honestly work quite well for this situation with just a little extra standardization. Audio codecs: use a single stream of whatever codec you'd like. FLAC/Vorbis/MP3/AAC/Opus/etc. can all go into Matroska. Seekable: Use chapters for tracks, and nested chapters for indices. Matroska documentation even gives an example of using ChapterPhysicalEquiv 20 fo…

Nested chapters can work for index markers, especially if a player supports them right. I mean: As mentioned, these have almost never been usable with real CD players in the wild. Maybe not much is lost there. (But the format must still accept these things, and allow them to be usable! An archival format must respect all aspects of the item being archived, including those that are unpopular or disused. I am willing t…

Interesting point about CD+G. I think whatever format was used needs to take this into account.

There were also a ton of Audio CDs that were not CD+G but had a data track with the music video etc on them.

I worked on a horrible one for Sony, one of those ones with all the anti-rip protection on it, where I was tasked to build a binary blob for a web site that detected if the specific audio CD was in your drive and let you into the web site. What were those things called, ActiveX?

Re: How CD pregaps gained their hidden track superpowers

#132

Post by sumtechguy »

qingcharles wrote: post #130
sumtechguy wrote: post #99

Earlier quoted context omitted.

You are almost describing the MAME CHD format. As they have the problem that the object (hard drive, cd, dvd, etc) must be in one file. Have the ability to do differences (writable in some cases). But also compressed (compressed hunks of data). They also need that sub track data too as some systems do interesting things with that sub data. As some even hide their encryption format in the SBI fields. The CHD format is…

This could be a good avenue. It might be possible the CHD format could be extended and be backward-compatible, or even just as simple as bodging all the extra data onto the end of the file and hope it is ignored by other readers. This is an avenue worth exploring, thank you.

There is a way to extend the format. As it has version number. It does have some metadata fields (drive geometry, compression formats, version of mame created with, etc). The trick would be getting the MAME team to accept the changes. Just dumping it on the end of the file I would guess they would not be too happy with.

There are a number of requests out there to extend the chd format and fix a few things. They are currently tracking some of this info in XML files (called hash files). They would be down with more accurate information though. So you would need a proposal that adds more accurate information and gives them something to work with. More like getting all the info that something like the redump project tracks in there would make them very happy.

There is a separate project that some other emus use libchdr which is a soft fork of MAME. I think they are trying to track closely to what the MAME group is doing but let other emus use it.

Re: How CD pregaps gained their hidden track superpowers

#133

Post by IndySun »

IndySun wrote: post #123
caf wrote: post #74

Earlier quoted context omitted.

Billy Eilish's latest is intended to be listened as a complete album (but of course the fact that this is known as an exception proves the general rule...)

Billy Eilish is not exceptional in this regard. 100s of 1000s of albums are. There's absolutely no need to single out an artist.

?

Re: How CD pregaps gained their hidden track superpowers

#134

Post by mmmlinux »

meindnoch wrote: post #107
AkBKukU wrote: post #102

Earlier quoted context omitted.

I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools. On your pregap + 99 indexes remark, the "pregap" is the space between index 00 and 01 which continues on up to index 99. Players seek to index 01 as the start point of the track. There is no separate pregap d…

>I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools. E.g. the Japanese version of Flying Lotus' album "Until The Quiet Comes" has a pregap of 5 seconds before the 19th track, to separate it from the rest of the album, as it's a Japanese-exclusive bonus track.

Is it crowd noise or just a gap? I'm also interested to see one of these skipable crowd noise CDs.

Re: How CD pregaps gained their hidden track superpowers

#135

Post by Elidrake24 »

Lammy wrote: post #20
dec0dedab0de wrote: post #14

I remember my friend accidentally found the negative track on a CD and called me up out of breath like aliens just landed. I think it was one of the early AFI albums.We spent the whole weekend checking for negative tracks on every CD we could find. The negatives between songs were also pretty cool sometimes, Mediocre Generica by Leftover Crack makes very good use of them. Listening to it over streaming or even mp3s r…

> I think it was one of the early AFI albums I wouldn't call it an “early” album but I found one of these (untitled 18-second intro) on AFI - DECEMBERUNDERGROUND: https://i.imgur.com/XAsFMSR.png Some others I've run across in my CD collection include… — on Jonathan Katz - Caffeinated https://i.imgur.com/4ghQadv.jpeg — the track "Every Time Is The Last Time" on Bloc Party's Silent Alarm https://i.imgur.com/knhbZhA.png…

Very Proud of Ya: https://en.m.wikipedia.org/wiki/List_of_albums_with_tracks_h...

Re: How CD pregaps gained their hidden track superpowers

#136

Post by sho »

d332 wrote: post #23

This inspired me to read up on the low-level details of CD structure. I'm curious if anybody scanned an entire CD and shared the results, so that we could work with a raw image of disc that contains all its quirks, as opposed to the typical .iso format?

Coming back to this, having read some of the (great!) replies, I'm going to go out on a limb and say that in theory, this sounds possible, and fun, but highly impractical. I'll assume that by "scan" you mean a high end "flatbed scanner" optical scan which would return a 2D bitmap.

It's impractical because the resolution required to retrieve the data "flatbed scanner style" is comically high, perhaps 50k dpi, far beyond the capability of any commercial unit and well into scanning microscope territory. Sure, from my understanding, it looks technically possible. But it would be a very significant and costly project just to assemble the image in the first place. Even if you had that, the resulting file would be hilariously huge (something like 122GB), extremely difficult to work with, and you would be starting from scratch implementing some kind of visual pathfinding helical decoder to painstakingly unravel the linear coil of data the scan just sort of blatted into two dimensions.

It's a cool idea. But it's comically, exponentially harder than just using the equipment as intended to just read the laser returns off the disk directly, into a far, far more easily dealt with format.

I'm adding that CD scan to my list of things I'd like to do if I ever get really rich.

Re: How CD pregaps gained their hidden track superpowers

#137

Post by ssl-3 »

qingcharles wrote: post #131
ssl-3 wrote: post #95

Earlier quoted context omitted.

Nested chapters can work for index markers, especially if a player supports them right. I mean: As mentioned, these have almost never been usable with real CD players in the wild. Maybe not much is lost there. (But the format must still accept these things, and allow them to be usable! An archival format must respect all aspects of the item being archived, including those that are unpopular or disused. I am willing t…

Interesting point about CD+G. I think whatever format was used needs to take this into account. There were also a ton of Audio CDs that were not CD+G but had a data track with the music video etc on them. I worked on a horrible one for Sony, one of those ones with all the anti-rip protection on it, where I was tasked to build a binary blob for a web site that detected if the specific audio CD was in your drive and le…

Sony had plenty of awful stuff at different times for audio CDs, despite being a co-developer of this wildly-successful and long-lasting format.

I think you're referring to ActiveX, yes. It's the only thing I can think of where "web" stuff and "hardware" stuff commingled back then in a semi-transparent way.

And famously, as you surely know yourself, Sony once published some rootkitted audio CDs: https://en.wikipedia.org/wiki/List_of_compact_discs_sold_wit...

Anyway, I'll just assume that you aren't the rootkit guy -- or even if you are, that your heart is in the right place.

---

And yes, CD+G is is important. As are the mixed-mode releases with video. All things CD audio are important if we are to talk about an ideal archival (and playback!) format for audio CDs, and archiving an audio CD is not always quite as simple as ripping a folder of FLACs -- there's a ton of diversity here that FLAC (and cue) can't accurately embody.

We're fortunate that we still have so many CDs right now, and that they're still being sold today. This will change. (It must change. It can't not change.)

The good folks working on the Domesday Duplicator have a relatively uphill battle for the often-older (and often rotting) LaserDisc media that they're working on tools to properly preserve.

It would be good to get ahead of the curve and get something with a practical workflow working sooner instead of later.

Re: How CD pregaps gained their hidden track superpowers

#138

Post by hcs »

AkBKukU wrote: post #102
ssl-3 wrote: post #29

One less-secretive way I've seen pregaps used is for live recordings. The crowd noise betwixt songs can be contained in a pregap, so that it is only ever heard when listening to the album straight-through (instead of in shuffle or track-program mode). --- Another fun feature of audio CDs is indexes. A disc can have 99 tracks, and each track can have some pregap (including track 1, as the article discusses). And each…

I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools. On your pregap + 99 indexes remark, the "pregap" is the space between index 00 and 01 which continues on up to index 99. Players seek to index 01 as the start point of the track. There is no separate pregap d…

Not sure why I didn't think to mention this before: One tool you might consider is redumper, it's designed in particular to handle multisession CDs, and it attempts to over-read into the disc lead-in and lead-out to catch data outside of the range covered in the TOC (particularly common in older CDs). It only outputs a final split bin+cue, but everything read, including scrambled data, toc, and subchannel/subcode, is saved for future processing. The bin+cue can be used with ISO Buster (and probably other tools) to access Enhanced CD filesystems. Feel free to reach out if you need some tips, this is what I use for my collection.

https://github.com/superg/redumper/

Caveat: It is mostly intended for use with the low-level features of Plextor drives, so CD support on other drives is relatively limited; in particular it doesn't have any overlapping read paranoia-style features. The recommendation is to dump twice to confirm; it's running straight through without seeking so that's usually still quite fast.

Post reply on HN