On Wed, Aug 20, 2014 at 10:30 AM, IOhannes m zmoelnig <[email protected]>
wrote:
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> On 2014-08-19 22:09, Alexandros Drymonitis wrote:
> >
> > Here's my perform routine: t_int *vanDerPol_perform(t_int *w) { //
> > Copy the object pointer t_vanDerPol *x = (t_vanDerPol *) (w[1]);
> >
> > // Copy signal vector pointers t_float *frequency = (t_float *)
> > (w[2]); t_float *factor = (t_float*) (w[3]); t_float *excitor_freq
> > = (t_float*) (w[4]); t_float *excitor_amp = (t_float*) (w[5]);
> > t_float *output = (t_float *) (w[6]);
>
> the scalar type for signals is really *t_sample*.
> you should NOT use *t_float* for these kind of things (though in
> practice they two might always be the same).
> if you are following a tutorial that suggests to use t_float, then
> report a bug to the author of the tutorial.
>
OK, changed it.
>
> >
> > // Copy the signal vector size t_int n = w[7];
> >
> > // Dereference components from the object structure float twopi =
> > x->x_twopi;
>
> now that looks very much like a constant, which you don't need to
> modify per-object...
>
I'm setting its value in the new instance routine by multiplying atan(1.0)
by 8, instead of writing it as a macro.
>
> > // excitor code si = *excitor_freq++ * si_factor; phase_local =
> > phase / step; drive_sine = cos(phase_local * twopi) *
> > *excitor_amp++;
>
> i guess you are copying the CSound code here.
> however, i really think it would be much better to use an "external"
> excitor, that is: instead of having an input for the frequency and
> another input for the amplitude of the internal sine oscillator, you
> might want to have a single input for an in-patch sine-oscillator.
>
> so your patch would look like:
> |
> [osc~ 666]
> |
> [*~ 0.42]
> |
> [vanderpol~]
> |
>
> (it might make sense to make the excitor input the first one, so you
> can use it
>
> this has two huge advantages:
> #1 Pd's oscillator is known to work; if it ever breaks, it will be
> fixed immediately.
> thus you don't need to re-code existing functionality, possibly
> introducing bugs.
>
> #2 you might want to use another exciter waveform, and get results
> unheard of.
> without any additional coding effort! for free!!
>
Did that as well.
>
> >
> > // van der Pol code c = 2 - 2 * cos(*frequency++ * twopi / sr);
>
> again, it might be better to use an external signal to drive this
> oscillator.
>
How? Can you provide a patch example? Or should I just translate this in an
abstraction?
>
>
> > aa = (-c) * ax + *factor++ * (1 - ax * ax) * av; av += aa; ax = ax
> > + av + drive_sine; *output++ = av;
>
> hmm.
> you are resetting "av" and "ax" to 0 for each DSP-block.
> most likely this is not what you want, as the srtucture looks like a
> feedback filter (IIR), so you need to store ax&av between DSP-blocks.
>
Fixed that too and the result is indeed much better. I don't think though
that this implementation is good. The output doesn't really look like the
example one finds online.
I've attached the .c file if anyone wants to take a look.
>
>
> fgmsdar
> IOhannes
>
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/******************************************
* van der Pol oscillator *
* translated from CSound's FLOSS manuals *
* written by Alexandros Drymonitis *
******************************************/
// Header files required by Pure Data
#include "m_pd.h"
#include "math.h"
// The class pointer
static t_class *van_der_Pol_class;
// The object structure
typedef struct _van_der_Pol {
// The Pd object
t_object obj;
// Convert floats to signals
t_float x_f;
// Other variables
t_float x_twopi;
t_float x_sr;
t_float x_av;
t_float x_ax;
} t_van_der_Pol;
// Function prototypes
void *van_der_Pol_new(void);
void van_der_Pol_dsp(t_van_der_Pol *x, t_signal **sp);
t_int *van_der_Pol_perform(t_int *w);
// The Pd class definition function
void van_der_Pol_tilde_setup(void)
{
// Initialize the class
van_der_Pol_class = class_new(gensym("van_der_Pol~"), (t_newmethod)van_der_Pol_new, 0, sizeof(t_van_der_Pol), 0, 0);
// Specify signal input, with automatic float to signal conversion
CLASS_MAINSIGNALIN(van_der_Pol_class, t_van_der_Pol, x_f);
// Bind the DSP method, which is called when the DACs are turned on
class_addmethod(van_der_Pol_class, (t_method)van_der_Pol_dsp, gensym("dsp"), A_CANT, 0);
// Print authorship to Pd window
post("van_der_Pol~: van der Pol oscillator, translated from CSound's FLOSS manuals\n written by Alexandros Drymonitis");
}
// The new instance routine
void *van_der_Pol_new(void)
{
// Basic object setup
// Instantiate a new vanDerPol~ object
t_van_der_Pol *x = (t_van_der_Pol *) pd_new(van_der_Pol_class);
// Create two addition signal inlets
inlet_new(&x->obj, &x->obj.ob_pd, gensym("signal"), gensym("signal"));
inlet_new(&x->obj, &x->obj.ob_pd, gensym("signal"), gensym("signal"));
// Create one signal outlet
outlet_new(&x->obj, gensym("signal"));
// Initialize 2pi and the oscillator's samples
x->x_twopi = 8 * atan(1.0);
x->x_av = 0;
x->x_ax = 0;
// get system's sampling rate and set sampling interval and factor
x->x_sr = sys_getsr();
// Return a pointer to the new object
return x;
}
// The perform routine
t_int *van_der_Pol_perform(t_int *w)
{
// Copy the object pointer
t_van_der_Pol *x = (t_van_der_Pol *) (w[1]);
// Copy signal vector pointers
t_sample *excitor = (t_sample*) (w[2]);
t_sample *frequency = (t_sample *) (w[3]);
t_sample *factor = (t_sample*) (w[4]);
t_sample *output = (t_sample *) (w[5]);
// Copy the signal vector size
t_int n = w[6];
// Dereference components from the object structure
float twopi = x->x_twopi;
float sr = x->x_sr;
float av = x->x_av;
float ax = x->x_ax;
// Local variables
float aa;
// damping factor
float c;
// Perform the DSP loop
while(n--){
c = 2 - 2 * cos(*frequency++ * twopi / sr);
aa = (-c) * ax + *factor++ * (1 - ax * ax) * av;
av += aa;
ax = ax + av + *excitor++;
*output++ = av;
}
// Reset object's variables
x->x_av = av;
x->x_ax = ax;
// Return the next address in the DSP chain
return w + 7;
}
// The DSP method
void van_der_Pol_dsp(t_van_der_Pol *x, t_signal **sp)
{
// Check if samplerate has changed
if(x->x_sr != sp[0]->s_sr){
if(! sp[0]->s_sr){
error("zero sampling rate!");
return;
}
x->x_sr = sp[0]->s_sr;
}
/* Attach the object to the DSP chain, passing the DSP routine vanDerPol_perform(),
inlet and outlet pointers, and the signal vector size */
dsp_add(van_der_Pol_perform, 6, x, sp[0]->s_vec, sp[1]->s_vec, sp[2]->s_vec, sp[3]->s_vec, sp[0]->s_n);
}
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