Random Thoughts

Emacs PCM Editing

I buy quite a lot of vinyl still.  And the hipsterish hipsters have started releasing things on tape, since vinyl is obviously too mainstream.  (I’m wondering when 78s will be making a comeback.)  So to listen to this music I need to sample it and then convert it to flac.

That’s trivial enough since I have a very nice DA, but the main issue is editing the music after sampling it.  I have, perhaps needless to say at this point, written an Emacs mode to do this.

As you can see, the mode is pretty self-explanatory.  It shows the wave forms, and you can zoom and set break points, and split the file up into pieces.  (Then name the files after querying freedb, possibly.)

The mode consist of one Emacs Lisp file and two C programs.  The first, summarize, goes through the PCM file and outputs the “energy level” in each section.  The second, bsplit, is just a fast file splitter. Oh, and there’s a patch to aplay to allow –-seeking to an arbitrary place so that you can skip around in the file and start playing sound at point.  (I see that I’ve forgotten to submit the patch to the ALSA people, so I did that just now.)

The interesting bit about wave.el is that it provides auto-splitting capabilities.  Or at least, it tries to.  It originally had a command for trying to put splitting marks at all points where the sound was “silent” for more than four seconds.  This worked somewhat OK, but what’s “silent” varies from sound source to sound source.  Some tapes are quite hissy.  And when I got a new record player, the background noise level dropped to almost nothing, so calibrating “silence” is boring.

Then I thought of a new approach: I know how many tracks there are in each file.  Say it’s a record album side with five sounds.  Then I could tell wave.el “this is five tracks, try to find a likely partition”.  It should snip away the initual “stylus hits the album” bump, and trim away the silence at the end, but otherwise put four sectional marks in the sound where it separates the tracks optimally.

However, I just wasn’t able to implement that in a satisfactory way.  The current wave.el isn’t really usable in automatic mode.

When you look at the sound files visually, it’s pretty obvious to a human bean where the tracks are, usually.  But I’m just not able to figure out a nice algorithm.  (I mean, I haven’t really tried a lot.  I think I spent a day on it last summer, if I remember correctly.)

If anybody has any ideas, I’m all ears.

Adam mentioned MusicBrainz in the comments of the last article.  I took that as a challenge, of course.

I only implemented the query bits, though.  I’m selfish.

(Oh, OK, the only reason I didn’t do the submission part, too, is that I can’t make up my mind whether cddb.el and musicbrainz.el should share the same editing mode or not.  I think perhaps.)

[Update: That felt like a cop-out, so I’ve started implementing MusicBrainz submitting.  I needed some way to get a MusicBrainz-compatible CD Table-Of-Contents listing, so I hacked up cd-discid to do that.]

The new album New Album from the folk band Boris

When ripping large quantities of CDs, you really have to have an efficient way to query and edit CDDB entries.  So here’s an Emacs library for doing that. It includes a bunch of convenience functions for fixing up other people’s bad entries, and you also have all the standard Emacs editing commands at your, er, command, so it’s rather nice.

I also download the entire database from freedb now and then.  It’s useful mainly when sampling (old) vinyl.  By using an approximate match for the albums, I can usually find the album in question, which means less typing for me.

However, the DISCID collisions these days are just ridiculous.  I’ve written about this before, but the situation is as ridiculous today as ever.  I mean, even more so.  It’s now impossible to submit any new album on the “rock” category, so everything I submit now is apparently “folk” or “data”.

As demonstrated.