Author Topic: estimate BPM and portamento  (Read 4309 times)

Offline Zenon

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estimate BPM and portamento
« on: July 13, 2010, 20:00:54 »
Hi all,
I would like to know the exact formula to get the extimated BPM (for what I suppose, it's a combo of tempo, ticks and row.

I've made this question because in a mod/xm I can't do an exact tone shifting by tone, so it's necessary (but honestly I'm not sure of this) to know first the  speed of the song in that moment.

In that case, is there a mathematical solution to know what a X value of tone portamento will bring the note ?

Well I don't know if I was clear (I really doubt it :) ) but thanks for the attention :)

Offline Saga Musix

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estimate BPM and portamento
« Reply #1 on: July 13, 2010, 20:15:48 »
Depends on which tempo mode you use in your module...

Quote
I've made this question because in a mod/xm I can't do an exact tone shifting by tone, so it's necessary (but honestly I'm not sure of this) to know first the speed of the song in that moment.

I don't really understand what you want. What is "exact tone shifting"? It sounds to me like the 3xx (MOD/XM) or Gxx (S3M/IT) command is unknown to you...

Quote
In that case, is there a mathematical solution to know what a X value of tone portamento will bring the note ?

Yes. But it's rather confusing for MOD, and also for XM/IT if linear slides are disabled.
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Offline uncloned

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estimate BPM and portamento
« Reply #2 on: July 13, 2010, 21:09:27 »
I think I know what you are talking about.


In this song I approximated 36 notes per octave by pitch slides.
http://clones.soonlabel.com/mods/goose.zip

I had to do it by ear. It may be the only reliable way.

However, once you do find the proper timing it does stay the same for every note.

Offline Zenon

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estimate BPM and portamento
« Reply #3 on: July 15, 2010, 01:25:55 »
Quote from: "Jojo"
Depends on which tempo mode you use in your module...

I don't really understand what you want. What is "exact tone shifting"? It sounds to me like the 3xx (MOD/XM) or Gxx (S3M/IT) command is unknown to you...


I'll try to be  clearer :)

Thinking about my xrns (renoise format) to xm converter, I had to face the problem with the different way both formats deal the 1xx effect.
For example, in renoise, a xx value of 10 pitch up a tone by an half tone (this is what I mean for an exact tone shifting);
 in xm you'd probably get the tone you want in the easy way only by ear, as uncloned said above.
I already know 3xx command , but it works in a different way by filling the note column with the tone you want to reach.

Quote
In that case, is there a mathematical solution to know what a X value of tone portamento will bring the note ?


Yes. But it's rather confusing for MOD, and also for XM/IT if linear slides are disabled.[/quote]

Indeed.
but I wanted to find a solution / trick in order to get the closest conversion possibile.

Offline Paul Legovitch

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estimate BPM and portamento
« Reply #4 on: July 15, 2010, 08:39:34 »
I'm not an expert so correct me if I'm wrong, in XM, with linear frequency slides, 1xx works like this :
Code: [Select]
101 = +1/16 semi-tone per tick

110 = +1 semi-tone per tick

1CO = +12 semi-tones (1 octave) per tick (#10 * 12 = #C0)

It doesn't depend on the tempo/bpm (Fxx above 20) but on the number of tick per row, which is 6 by default and set by the command Fxx from 01 to 1F.

Little subtlety : F06 is 6 ticks/row but the 1xx effect is only applied 5 times per row (not applied on the first tick).

F01 or F02 -> effect applied only once per row.
F03 -> effect applied twice.
F04 -> effect applied 3 times.
F05 -> effect applied 4 times, etc.

So by default, with F06 (effect applied 5 times) it's not possible to reach exact semi-tones :
Code: [Select]
101 = +5/16 semi-tone per row.

103 = +15/16 semi-tone per row, wich is almost a semi-tone but not exact.


(in IT format there are fine and extra fine portamento commands to deal wit this pb but not in XM format afaik)

As for non-linear frequency slides, the effect of the portamento command depends on the frequency of the note : pure evil :evil: that's all I know.
But if it's for a xrns to XM converter you don't have to mess with this do you ? Just select linear frequency slides.

Offline Saga Musix

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estimate BPM and portamento
« Reply #5 on: July 15, 2010, 08:43:35 »
Looks about right. XM also has extra fine portamento, using the commands X1x and X2x.
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Offline Zenon

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estimate BPM and portamento
« Reply #6 on: July 15, 2010, 19:49:30 »
Thanks a lot Paul, is pretty much clear now!  :P
Jojo, can you explain why I can't hear nothing different when I use fine portamento command in xm?

Even if I try to put a value of x1 or xf after a note I listen always the same tone  :shock:

Offline Saga Musix

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estimate BPM and portamento
« Reply #7 on: July 15, 2010, 21:36:30 »
Quote from: "Zenon"
Even if I try to put a value of x1 or xf after a note I listen always the same tone  :shock:

That sounds wrong.
X11 is the finest porta up, X12 is a bit more... X1F has the most effect.
Same goes for X21 through X2F.
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