[ID3 Dev] questions regarding TBPM frame.

[darien]

hey there Pyt ...

thanks for replying.

>Strictly speaking, TBPM is a text frame, so it is very possible for 
>it to be set to just about anything textual if a program would allow 
>it. However, the v2.4 spec is pretty clear that it is an integer and 
>that it is beats per minute, so you cannot set it to 123.45, and 
>even though you could set it to 12345, but that would probably 
>meaningless from a musical standpoint...
>
>I guess your programmer must have decided that more than 999 beats 
>per minute is nonsense, which can be understood but is indeed going 
>a bit further than the spec intends.
>
>Not sure this helps...

it sort of does ... it's brought a couple of things to light, and i 
have a question...

how does one go about getting the spec for the TBPM frame changed to 
allow for a decimal place and 'non-whole' bpm measurements (ie 
132.68, 95.35, etc) as allowable and legitimate data for the spec?

i feel that it's not right the way it is, i can think of quite a few 
arguments for why the 'standard' should be changed to allow a decimal 
place if desired or needed, and i'd like to push to have it changed. 
it would make my life a bit easier in a few different ways, and i 
reckon it would probably help other people out there as well.

bpm measurement is *never* a solid, honest-to-goodness integer. well, 
not practically, anyway. it's usually measured in averages, because 
there are no recordings out there that are perfectly on-beat from 
start to finish ... there are many obvious reasons why... neither 
midi clocks nor human drummers are ever 100% on the money with regard 
to keeping time, hence having bpm measurements of 132.68, 95.35, etc. 
while midi clocks come close, there's always a little bit of slide 
with regard to the accuracy of its' generation. human drummers are 
never 100% -- every human drummer is always off the mark by some 
percentage (usually depending on how drunk they are). the only thing 
that is pretty much right-on is smpte, and a large percentage of 
professional musicians don't use smpte for clock generation (though 
there are a few out there that do, especially if they're working in 
hollywood on film or television projects).

most software applications that measure bpm properly do not end up 
with a bpm measurement that is a whole integer either (here's one i 
know of that's free and writes the value into the id3v2.x tag : 
http://www.mixmeister.com/download_freestuff.html ) ...

i'm a dance music dj and i play a lot of electronically-based music. 
i play house, prog house, hip hop, breaks, and i play some mobile dj 
gigs too if the money's right. years ago, i used to exclusively dj 
with vinyl records and cd's, but now i use traktor dj studio to dj 
with. traktor dj studio has the ability to be able to 
control/manipulate playback of mp3's using a special hardware audio 
interface and vinyl records with a recording of timecode cut onto 
them. the timecode records tell the computer what pitch the record is 
playing back at, where the needle is on the record and so forth. the 
records and hardware are essentially a control interface, and a 
brilliant one at that.

about 80% of the mp3's i generate to dj with are from recordings of 
vinyl records, because that's the medium of choice for dj'ing 
electronic music -- a lot of prime stuff gets released on vinyl that 
never sees a digital release, even in this digital world of ours. 
vinyl, as a rule, is an imperfect medium, which opens up a pretty 
huge can o' worms in itself with regard to bpm and speed in general. 
here are some examples of things that cause timing issues with vinyl records:

o - vinyl records are never perfectly flat. every record pressed 
(even a 180 gram audiophile grade record) has a certain degree of 
warp to it. they can be really close to flat, but never perfectly flat
o - the stamper plates used to press records are made of nickel, and 
a high amount of pressure is placed on them for every record pressed 
-- it takes 120 tons of pressure to press a vinyl record. as a 
result, every pressing degrades the stampers slightly. stampers are 
only good for 1000 pressings. after that, the stampers will have 
degraded enough to create a noticably imperfect product and a new set 
of stampers must be used.
o - consistency of the vinyl material differs slightly from batch to batch

couple these factors with a midi clock that doesn't generate time 
perfectly and you've got a recording that isn't going to be anywhere 
near perfect, timing and bpm measurement-wise.

this is just one example. another that i could explore is disco or 
funk tracks from the 70's... parliament, the bee gee's, gloria 
gaynor, cheryl lynn, donna summer, etc. all of that stuff was 
recorded onto analog tape, and human drummers were employed. analog 
tape stretches and shrinks with temperature and general use. tape 
machines of the day weren't digitally regulated, and no analog motor 
is perfect. pair those imperfections with a human drummer and loads 
of disco or funk swing, and you've got a recording that isn't 
anywhere near a whole integer bpm-wise.

so yeah ... some good arguments there. ;)

any advice on how to go about getting the spec changed for the TBPM 
field would be greatly appreciated.

cheers.

--darien!



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