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Topic: BPM scanner consistently wrong for all new (higher quality) rips

This topic is old and might contain outdated or incorrect information.

Hi,

OK, here's what's happening to my BPM scanner:

BPM scanner is getting the BPM wrong for ALL my newly ripped CD tracks.

I've never had a problem with BPM scanner before. In the last two weeks, I've spent countless hours re-ripping my CD collection using JRiver with LAME MP3 encoder + 'Secure Mode' and also a brand new DVD drive. My previous rips were done with Windows Media Player. The new rips, plus copies of all my downloaded MP3 files (I've got roughly an equal amount of both) were put in a new folder structure. The MP3s sound great, so no problem there. I've also spent a long time attaching the correct artwork, artist, album, genre etc to the files, so I'm very keen to find a solution to the situation I now find myself in :)

BPM scanner is getting the BPM wrong for ALL my newly ripped CD tracks :( The BPM scanner is giving the same tracks in the new library a lower BPM (e.g. 137.5 instead of 138).
The downloaded MP3s are fine, and display precisely the same BPM as in my old library.


Additional information:

Took me a while to figure out how the BPM in the XML database relates to the 'actual' BPM value.

The XML 'BPM' is "the number of samples at 44.1kHz between two beats"

The conversion formula is:
actualBpm=60*sampleFrequency/xmlValue
i.e. actualBpm=60*44100/xmlValue

(I believe that practically all MP3s have sample frequency of 44.1kHz - please someone correct me if I'm wrong).

In the new XML database, the Bpm value is approximately 1.005 times the corresponding value in the old database (i.e. 1.005 times the correct value). But this varies slightly from track to track. Here is a selection of ratios of new to old library track BPM data:

1.0054879265615645579724605867092
1.0052589213844915481620606385833
1.0039682539682539682539682539683
1.0039637008448941274642745384375

I've spent a lot of time getting the best quality rips I can and organising my library. The only thing I can think of, is that Virtual DJ BPM scanner doesn't like something in the JRiver LAME encoder, or perhaps assumes something about it that isn't the case?

This is a disaster for me. Please, if anyone can help I'll be very grateful.
I'll post some additional information later.
Thanks,
Nick
 
Posted Fri 19 Jul 13 @ 8:48 pm
Downloaded MP3s from old and new libraries give identical XML BPM values (see below)

Downloaded MP3s from old library:
XML BPM
19456 Progressive Psy Trance Picks 2011 Vol.1\25 - Rise.mp3
19456 Progressive Psy Trance Picks Vol.7\02 - Goofy Jam Session.mp3
18900 Dave Pearce Trance Anthems 2009\60 - The Burn (Manuel Le Seux Remix).mp3
19630 Trance\28 - Meet Her At The Love Parade.mp3
19316 Dragonfly\Dragonfly Classix Disc 1\02 - LSD.mp3
21000 Ibiza Closing Party Classics\19 - Hay Consuelo (Samim Remix).mp3
19174 Progressive Psy Trance Picks 2011 Vol.1\03 - Ask The Right Questions.mp3
20672 Global Progressive Trance Sessions Vol. 1\04 - Moment of Sunrise (EDU Remix).mp3

Downloaded MP3s from new library:
XML BPM
19456 Progressive Psy Trance Picks 2011 Vol 1\Philter - Rise.mp3
19456 Progressive Psy Trance Picks Vol 7\Neelix - Goofy Jam Session.mp3
18900 Dave Pearce Trance Anthems 2009\Simon Hunt - The Burn (Manuel Le Seux Remix).mp3
19630 Trance\Da Hool - Meet Her At The Love Parade.mp3
19316 Dragonfly\Dragonfly Classix Disc 1\Hallucinogen - LSD.mp3
21000 Ibiza Closing Party Classics\Pier Bucci - Hay Consuelo (Samim Remix).mp3
19174 Progressive Psy Trance Picks 2011 Vol 1\Neelix - Ask The Right Questions.mp3
20672 Global Progressive Trance Sessions Vol 1\Origin - Moment of Sunrise (EDU Remix).mp3
 
CD Rip MP3s from old and new libraries give different XML BPM values (values are correct in old library)

CD Rip MP3s from old library:
XML BPM
20044 101 Trance Anthems Disc 5\07 La.mp3
19476 Psychedelic Gate, Vol. 2 Disc 2\05 Shamanda.mp3
18635 Alien Project\Aztechno Dream\07 Skunk.mp3
18636 React\Reactivate, Vol. 7 Aquasonic Trance\08 Darkstar.mp3
25929 Dimension 5\Transdimensional\10 Flow.mp3

CD Rip MP3s from new library:
XML BPM
20154 101 Trance Anthems Disc 5\Marc Et Claude La - La.mp3
19776 Psychedelic Gate 2 Disc 2\Akasha Project - Shamanda.mp3
18733 Alien Project\Aztechno Dream\Alien Project - Skunk.mp3
18734 React\Reactivate 7\Nico - Darkstar.mp3
26205 Dimension 5\Transdimensional\Dimension 5 - Flow.mp3
 
The VDJPEDIA says there's a choice of two algorithms for BPM scanning:

==Manual BPM Correction==

The CBG is calculated automatically when a track is loaded for the first time. VirtualDJ uses powerful algorithms to calculate the BPM and the CBG of music (1 of 2 algorithms can be chosen - a fast but effective algorithm which works well for techno and house, and a slower algorithm which is effective on any type of music).

Unable to find it in options screens or in a config file anywhere.
Anyone know where it is?

Cheers,
Nick
 
I think I've found out what's going on :)

JRiver also calculates BPMs (not so accurately) and writes them in the MP3 tags.
Virtual DJ, when scanning for BPMs, looks at the BPM tag and bases its calculation on the value read, by assuming it's close enough and 'fine tuning' the BPM. I guess that if the tag BPM isn't close enough then Virtual DJ *NEVER* manages to accurately calculate the BPM.

At the weekend I did actually try removing a file's BPM tag value and rescanning, but it didn't help. The BPM tag value must be removed BEFORE virtual DJ adds the file to its XML Database (otherwise something about the BPM tag is persistant in the XML Database: pre-scan this is 'BpmTag' value; not sure what it is post-scan).

So if your BPM scans are coming out wrong, then check your MP3 BPM tags.

Nick
 
If BPM is set in the tags of the file then VirtualDJ will assume that this value is correct and will use it, overriding its own calculation during analysis of the file. This is because many DJ's will correctly tag their files including setting the correct BPM before using them with various DJ software. Also, purchased songs from DJ record pools and similar services will usually have the correct BPM already embedded.

If the value stored in the tag is incorrect after adding it to VirtualDJ's database, then you will need to manually correct it, e.g: By tapping on the BPM button of the default skin, or right-click on it and type in the correct value (If known.)

If the ripping software that you are using does not accurately calculate BPM, then you should disable it writing this to the tag if it has this option.
 


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