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Faster display of BPM when starting timecode cd

PostPosted: 13 Jul 2011, 04:20
by pundy
I'm using CDJ 800s with the start delay set at minimum. (so when I hit play there is no ramp up to speed of the playing track). In Cross however, the BPM (and the waveform display) seems to ramp up to speed. (takes a second or two maybe) Now the track itself doesn't ramp up to speed, just the bpm display and waveform display.

This tells me two things:
1) that Cross knows almost instantaneously the speed that the timecode cd is running. (as the track playback doesn't ramp up like a turntable would)

2) that the display of BPM and waveform is based on some sliding window count of timecodes (number of timecodes over some predetermined window, then applied against the BPM of the actual track)

Apart from the ramp up of the number (and associated zoom in of the wave form), this means that minor adjustments of the cdj pitch fader take a little while to be reflected on the BPM display. This is quite annoying when trying sync the track speeds manually.

I don't really see why Cross needs to have the arbitrary ramp up of BPM / zoom in of the waveform. Would it be possible for these displays to be as instantaneous as the actual BPM that the track is playing at?

Re: Faster display of BPM when starting timecode cd

PostPosted: 13 Jul 2011, 06:18
by Blackbrook
If you are asking me the BPM is a reslut of an averaging and therefore it is not possible to change it.
If you think of your CDJ 800 they will work the same way (my CDJ 200 did). Changing the pitch fader does not mean that the BPM on the CDJ changes instantly. And by the way: CDJs just display even BPMs i.e. 129, 130,...

I did not understand why this is a problem for beat matching or syncing. Can you please say something more about it?! Thanks!

Cheers,

Steve

Re: Faster display of BPM when starting timecode cd

PostPosted: 13 Jul 2011, 07:31
by pundy
It isn't *really* a problem for beat matching - after all you can just wait a second or two for the display to catch up and then adjust from there right. Or even yet not even look at the screen and do it by ear. But that isn't the point.

You are right in saying CDJs don't display instantaneous BPM on start, but that is because they are doing BPM calculations on the fly by analysing the track. You'll notice that the BPM changes on a CDJ as the music does, implying that its not a full track analysis leading to a single number.

Cross is slightly different. (from my understanding)
It pre analyses tracks and calculates a static BPM for the file. It then calculates the required tempo from the timecodes on the CD. The display shouldn't have to ramp up for Cross - it should be known as soon as the BPM from the timecode track is calculated. (which has to be in the order or 1-2 milliseconds since you have a 3kHz timecode track and you'd only need a handful of codes to determine the current cd temp). As soon as you know CD tempo, its a quick calculation to apply this to the actual track.

Cross must know almost instantly the timecode tempo as the sound doesn't ramp up to speed on play like a turntable would. (implying two different calculations for the "current speed") So why does the display have to be like that?

(of course if Cross is doing some frequency based peak analysis to determine BPM on the fly, then my argument goes out the window! :redface: )

Re: Faster display of BPM when starting timecode cd

PostPosted: 13 Jul 2011, 09:44
by sylMV
Hi!

Thanx for your message.

No of course you're right, BPM isn't computed on the fly.

The reason why the BPM display takes a short time to reach the current value is that it doesn't display the instantaneous value, but a smoothed one. Why ? Because the detected timecode speed is never perfectly stable. With TC CD, I agree there are only small variations, but Cross also handle TC Vinyls that have far less stable speed... That's a complicated problem for which we tried to find an acceptable compromise (CD vs Vinyl). But I find your point of view very relevant and make me think we should maybe try to improve this behavior for TC CD ...

Cheers,

Re: Faster display of BPM when starting timecode cd

PostPosted: 14 Jul 2011, 01:08
by pundy
Ahh I see. So basically since the timecodes in the input signal aren't perfect, you've smoothed the values so they don't jump all over the place all the time.

I'd love the ability to pull the display smoothing down to as accurate as the playback numbers. Of course I'm wary of too many user selectable options, as I imagine you guys are also. Perhaps in the preferences where I set up the timecode medium (MV CD or MV Vinyl), if the CD is selected the smoothing could be made more equivalent to playback? This way CDs would be tight, and vinyl could still be smooth.

To be honest I don't *really* mind the initial ramp up when hitting play on CDJ, I find I'm usually listening to the track more then. The thing that bugs me is moving the pitch slider and having to wait that "little bit too long" to see the values reflected on the BPM counter.

Re: Faster display of BPM when starting timecode cd

PostPosted: 09 Aug 2011, 08:58
by skandal
Hi, I find this a good remark.
I'm using the TC Vynils and encounter the same problem.
Ideally the BPM speed should be shown immediately. Even when the turntable is not spinning. Now, you should first start the turntable, wait 2 secs before you can see the current bpm speed.

I believe it would be a good allround option to calculate the bpm on the fly or to choose having the bpm always shown (pitch already calculated with it)