Rockbox General > Rockbox General Discussion
what is "True random shuffle "
per01:
Hello all. Let me start by saying I really prefer Rockbox over my OF (Sansa Clip+ 8gb + 16gb card 3771 tracks Rockbox version 3.7). All of you are incredibly brilliant and I have a hard time understanding most of your posts as I am not an MIT educated engineer nor computer scientist (I am a lowly anally retentive tax accountant).
I do however have a knack for picking up patterns and although the shuffle may be a true random shuffle by definition, and is way better than Sansa's shuffle, I do notice a certain pattern during playback which can not be attributable to observation bias. I have neither graphed nor documented my conclusion so scientifically my theory can't be proven, you'll just have to take my word for it; or ignore this post completely. I just want to add my voice to those who have sensed that the shuffle function isn't as completely as random as it is defined to be.
Specifically, it appears to me that tracks off of a certain album or 2 (or 3) are somehow chosen to be interspersed with other apparently random chosen tracks. After every 7-10 or so random songs, another track off of one album pops up. In my most recent observation from this past week, even though I have many Grateful Dead songs on my Sansa, songs from "Postcards of the Hanging" are being played at least once every 1/2 hour. Two weeks ago is when I first noticed the pattern and I waited another week before I reached my conclusion and decided to publish my thoughts on your forum.
I am not imagining this phenomenon nor am I complaining about your programing skills (as I've said, you all are incredibly brilliant), I just wanted to share my experience.
Llorean:
--- Quote from: per01 on December 18, 2010, 07:54:34 AM ---Specifically, it appears to me that tracks off of a certain album or 2 (or 3) are somehow chosen to be interspersed with other apparently random chosen tracks. After every 7-10 or so random songs, another track off of one album pops up. In my most recent observation from this past week, even though I have many Grateful Dead songs on my Sansa, songs from "Postcards of the Hanging" are being played at least once every 1/2 hour.
--- End quote ---
What would shuffle be other than songs being interspersed with other random songs?
As soon as you hit shuffle, or choose "insert shuffled" or however you start your playback, you can immediately pause playback and view your playlist. If there's a significant distribution problem it should be relatively easy to check by creating even as few as a half dozen new playback situations.
I know you believe that your knack for pattern recognition means your position is unassailable, but whether this is true or not if this isn't a problem that can be demonstrated in the actual playlist files and not solely in the ears of the beholder it makes it more or less impossible to solve as there's nothing visible to begin tracking down.
per01:
I appreciate your devotion to Rockbox and your attempt to parse my post. That you even bothered to respond shows how much the Rockbox community cares about their product.
I never meant to imply that my "position is unassailable", my postion is very sailable ;). In fact, I'm really not even taking a position one way or the other. I just wanted to advise others of my experience and add my voice to those (if there are any others) Rockbox users that have a gut feeling that the shuffle feature may be playing one artist or album in less than random order.
I know it's not proper to read emotions into these types of things,but I sense a little anger in your reply. Please don't be angry at my original post, that's the last thing I wanted to do.
AlexP:
Gut feelings count for nothing.
Shuffle a playlist repeatedly, look at the distribution, do some statistics :) This is what soap did a few posts back, and the distribution was random. Until someone can prove otherwise, it is all just imagination.
Llorean:
No anger. At most skepticism.
You offered no information that suggested it wasn't selection bias. In fact you specifically said "I am not imagining this phenomenon" which is what gave me the impression you felt your position was solid. Proof that you aren't imagining it would be easy to come by - you could generate a number of playlists under identical conditions and look at how the files are distributed. As well you said it "can not be attributable to observation bias" but what you've described (I noticed a phenomenon and then when I looked for it, I found it) is almost a textbook way of describing observation bias.
Shuffle shuffles all the songs you've selected. It's entirely reasonable to expect to occasionally have 2 or 3 hours periods where many songs from one album show up. Especially if you have lots of music. Some albums will be distributed exactly evenly across the entire playlist, other ones will be "clustered" around points of time because random distribution means that it also won't force them not to be near each other.
As AlexP, Soap and I have said, it's basically trivial to test this in an objective way (rather than introducing the subjectivity of "what I remember hearing" and so on). You could do as little as generate a shuffled playlist of all music (describing in your post what method you used to do this) then go through the first 50 songs and note down the number of songs from each album. Do this about 20 times (re-generate a new shuffled playlist, count). Then calculate what percent of your music each album represents (number of songs in album divided by total number of songs in the playlist you generated) then what percent of those thousand tracks you counted were from each album (number of counted instances divided by 1000). This isn't particularly thorough but if there's a strong flaw in the shuffling algorithm to cause preference for certain folders it's fairly likely to show if it's something as easily observable as described above.
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