Hi!
Am 14.07.20 um 03:19 schrieb Tim Janik:
> the Blebsynth Filter range is currently created as 20..24000:
>
>> pid_cutoff_ = add_param ("Cutoff", "Cutoff", 20, 24000, 1000, "Hz", STANDARD
>> + "logcenter=880:");
>
> Those boundaries don't fit exactly for a straight logarithmic mapping like
> you gave in the comment below, if you also want a straight mapping of
> pixels to octaves (i.e. map 0..1 to an integer set of octaves).
I don't want an integer number of octaves - see below.
> The value range closest to the current boundaries that I could find is
> centered around F#5 (739.99Hz):
>
> begin=440 * 2**(9/12.) / 2**5. ; end= 440 * 2**(9/12.) * 2**5.
> print begin, end
> 23.1246514194771 23679.6430535446
>
> Let me know if I should use different boundaries when I'm implementing
> logarithmic parameters.
Is there a reason why you want to have "whole" octaves? Two examples for
possible cutoff ranges:
- 20..24000 corresponds to log(24000/20)/log(2) = 10.23 octaves
- 20..30000 corresponds to log(30000/20)/log(2) = 10.55 octaves
I don't see any reason to quantize the ranges as to enforce choosing
either 10 or 11 octaves instead of implementing the ranges exactly. As
long as the mapping is logarithmic it should be ok for the user for
automation and ui controls, even if we don't have an integer number of
octaves.
I would understand if for some reason you want to quantize the
lower/upper bound to an integer number midi note.
Cu... Stefan
>
>
> On 13.07.20 13:13, Stefan Westerfeld via beast wrote:
>> I have just added logscale mappings
>>
>> The mappings you added are obviously useful, especially for milliseconds
>> (x^3)
>> mappings, but these are /not logscale/. A true logscale mapping plots as
>> line if
>> you |set logscale y| in gnuplot. A true logscale mapping is fully determined
>> by
>> two points, a center is not necessary. Here is how that would compare to the
>> function you implemented:
>>
>> |begin=32.7; end=8372; center=523; e=log((end-begin) / (center-begin)) /
>> log(2)
>> print e; set logscale y; plot [0:1] begin + x**e * (end-begin), center, exp
>> (log
>> (begin) + x * (log (end) - log (begin))) |
>>
>> You can also see that this is not true logscale in BlepSynth frequency knob.
>> It
>> has more pixels for 20..40 Hz than it has for 12000..24000 Hz, even though
>> what
>> we wanted is that each octave takes the same number of pixels.
>>
>> —
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>
--
Stefan Westerfeld, http://space.twc.de/~stefan
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