Wednesday, May 24, 2006

Optimistic and Pessimistic Ranking Strategies

With computer algorithms related to performance, there are often variations known as "optimistic" and "pessimistic". That is, you figure out whether each operation is likely to be trouble-free or error-prone, and arrange things so that you don't waste a lot of time going down the wrong path.

I've run through a lot of different scenarios for ranking songs, and found that these complementary strategies can save plenty of time and aggravation if you use them wisely.


Let's start with the pessimistic technique, because I've found this applies in more kinds of situations. For me, it usually involves rating songs on the iPod while driving. It could also apply while listening to a particular playlist, particularly on shuffle play.

You should use this technique when you're listening to music that is unfamiliar, or from a genre that's not your favorite, or from a whole range of genres. You don't have any particular reason to expect great things from each song. You might like an occasional song, but chances are that >50% will get a low rating.

With the pessimistic technique, as soon as the song starts playing, you give it a low rating. For me, "low" means 2 stars. That's the rating where I'll actually uncheck the songs so they don't get synched to the iPod or played on shuffle or sequential play.

With the iPod, this typically involves 2 presses of the center Select button, spin the wheel until you hear 2 clicks corresponding to stars, then you can either put down the iPod and or press the Select button one final time to go immediately back to the time display. Within iTunes, I'd recommend a utility like SizzlingKeys that lets you use a keyboard shortcut to assign an iTunes rating regardless of what application you're in.

With a little practice, it becomes automatic to assign the same low rating every time a new song starts playing, or immediately after you skip to a new song.

The key with this technique is that the moment a song starts to bore or annoy you, you skip to the next song without even a fraction of a second of unnecessary torment. The low rating becomes permanent, you assign the next low rating in the first 1-2 seconds before the next song can really get going, and most of the time this is all you need to do.

For those relatively rare cases where a song deserves a higher rating, you have to assign a new, higher rating later on during the song. But this is not so unpleasant to do for an enjoyable song. Since you expect most songs to get low ratings, it's more important to avoid going into a funk from listening too long to bad songs, or having to fumble with the rating controls before you can skip ahead.

This technique is appropriate for:
  • Diverse collections. I'm using it for rating songs from SXSW 2005, which featured hundreds of free songs across a wide range of genres.
  • Exploring an artist's back catalog. If the band isn't one of your favorites, you already know their hits, and just want to make sure all their other songs are rated, you can expect that most songs won't be all that good.
  • Taking a flyer on a new style of music. For example, if someone says "you really should try some" modern jazz, nu metal, world music from a place you've never heard of... In other words, some style that if you were actually going to like it, you'd probably know if already. Hey, you might be pleasantly surprised, and if >50% of the songs earn a good rating you can stop using this technique.


With the pessimistic technique, the priority is to get out of a bad song as fast as humanly possible. The optimistic technique uses the opposite approach, the idea being that most songs deserve a high rating and so should play all the way through without having to touch the rating controls.

Instead of assigning a (low) rating to each song as it begins to play, then bumping up the rating for the occasional good song, you assign high ratings to all the songs beforehand, and only lower them for the occasional bad song. There's an assumption here that these rare bad songs won't be especially bad -- maybe deserving 3 or 4 stars instead of 5 -- so it doesn't drive you nuts to keep listening while you bump down the rating.

This technique is appropriate for music that you are familiar with and have high expectations for:
  • A "Greatest Hits" album from a group you like.
  • A box set from one of your favorite groups.
  • An acclaimed album (critics' choice, or on some "greatest of all time" list), in a genre that you like.
  • A live concert, or collection of cover versions, where you already know the songs.
I usually save this technique for cases where the average rating is likely to be 4 stars (meaning it's much rarer than the "pessimistic" case above).

Because this technique involves assigning ratings in bulk before you even start listening, it's not appropriate to use with a Smart Playlist with the condition "My rating is blank". That's a great way to rate unfamiliar music, because as you rate each song it drops off the playlist, meaning you only hear each song once, until you've rated them all and the playlist is empty. But to do something similar for songs with pre-assigned, guesstimated ratings, you must get a bit fancier with Smart Playlists:
  1. Put the collection of songs you're rating into a standard playlist.
  2. Make a second playlist, this one a Smart Playlist, with "All" of these conditions: "Playlist is name of first playlist", "Play count is 0", "My Rating is ****" (or 3 or 5 stars, whatever you want to use as the default rating).
Now you can listen to this new Smart Playlist at leisure, with minimal need to fiddle with ratings. Once a song plays all the way through (and you leave its rating on the default setting), it'll drop off from the playlist. (I'm assuming here that you're rating these songs while listening to them for the first time.) If you decide to change the rating for a song, it'll also drop off the playlist. Listen long enough, and the playlist will become empty; all the songs will be rated, with minimal effort since most of them just keep the default rating you set up in advance.

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