Re: [Freecycle-users] interface questions

[Predrag Viceic]

Hi Piotr,

Well, that's a whole lotta good questions! I'll maybe consider writing a 
FAQ :)

Q: Could You tell me what is this popup menu with this kind of time signatures 
for? How to use it.

A: When the sound signal gets analysed, the bpm computation starts based on 
beatline positions. If there are at least 4 locked beatlines, only the locked 
beatlines serve as the basis for the bpm computation, If there are less than 
4 beatlines locked, the unlocked (green) beatlines are used. The value 
obtained is then multiplied by the values in the combo. That gives you the 
possibilitiy to change the detected 75BPM to i.e. 150 BPM. The computed value 
is then used for:

a) Time stretching
b) measure marker computation (the bar between two loop points, when dragged)
c) bpm lines computation (activated by the clock icon and at least one locked 
beatline)
c) midi file generation


Q: I would like to know what is the purpose of the clock button and why and 
when it becomes "active"

A: This icon gets enabled when there is at least one locked beatline. It draws 
what I call the bpmlines, i.e. the measures based on the BPM and synchronised 
with the first locked beatline.


Q: I guess that the time stretch amount is in percent, but why is the initial 
value 30 and not 100?

A: it is the BPM and not the percent.



Q: Does the beatlines and loop markers affect the bpm?

A: Beatlines are the basis for the BPM computation. Loop markers doesn't 
affect the BPM.



Q: How does the "time signature" pop up menu affect the bpm?

A:The detected bpm value is multiplied by the value in the combo.
i.e. 150BPM x 1/2 =75BPM


Q: Is it possible to stretch one beat in a whole loop?

A: For now, time stretching works on the whole sound file.



Q: What are the different analisys methods best for?

A: Well that's a short question with a huge answer. :)

The first (default) algorithm (time domain) detects beats by comparing the 
instant energy (nb of samples configured as instant energy buffer size in 
Configuration->Configure Amplitude Domain) with the average energy (nb of 
samples configured as avergage energy buffer size in Configuration->Configure 
Amplitude Domain). If the difference exceeds some treshold computed internaly 
and based on the variance of the signal, then the beatline is put at that 
position (well it's a little bit more complicated because Freecycle then does 
zero-crossing, but you should have got the point..)

The second algorithm (frequency domain) does the same thing but the signal is 
splitted in multiple bands and the algorithms compare the instant energy of 
each frequency band with the average energy of that band. That gives you the 
positibility to beatmatch the signal with continuous amplitude but varying 
frequency (flute playing legato notes). Configuration->Configure FFT-> 
Beatmatching FFT gives you the parameters for this algorithm. Window is 
equivalent to the [instant energy buffer size]. Average energy is hardcoded 
as 44032 frames.

If you want to know more about the above two algorithms please read the 
following [http://www.yov408.com/beat/BeatDetectionAlgorithms.pdf] as it 
served as the basis for these two algorithms.

The aubio algorithms are well known among DSP experts, which I'm not. Please 
search on the web if you want some precisions about those. Feel free to post 
your findings here. :)




Q: What is the fft configuration and configure amplitude domain menus for and 
how to set it for the best (depending on cpu and memory) program performance?

A: Generaly speaking slower->better and faster->less precise. Experiment! The 
default values are ok on a 2Ghz  CPU and 1Gb RAM. But this depends on the 
size of your soundfile, so if you keep those relatively small it should be ok 
even on less recent computers.

You can see the effect of fft configuration parameters in the spectrogram view 
(View->Spectrum). Spectrogram FFT parameters are used for drawing the 
spectrum. If you link those parameters to the Beatmnatching FFT, you cans see 
what the Frequency domain analysis algorithm "sees".


Cheers,
Predrag




> Hi Predrag,
> Could You tell me what is this popup menu with this kind of time
> signatures for?
> How to use it?
>
> Also I would like to know what is the purpose of the clock button and
> why and when it becomes "active"
>
> I guess that the time stretch amount is in percent, but why is the
> initial value 30 and not 100?
>
> Does the beatlines and loop markers affect the bpm?
>
> How does the "time signature" pop up menu affect the bpm?
>
> Is it possible to stretch one beat in a whole loop?
>
> What are the different analisys methods best for?
>
> What is the fft configuration and configure amplitude domain menus for
> and how to set it for the best (depending on cpu and memory) program
> performance?
>
> Thanks
> Piotr
>
>
> --
> Kopalnia Dzwieku
> Piotr Karol Sawicki email: address@hidden
> strona domowa: www.piotr.art.pl
> gg: 8976726
> jabber ID: address@hidden
>
>
>
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> Freecycle-users mailing list
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