tomwalters@0: /*
tomwalters@0:   ramp.c    generate an exponential sawtooth waveform
tomwalters@0:   ------    (in binary shorts or floats).
tomwalters@0: 
tomwalters@0:     Generate samples of a sawtooth waveform at a given sample rate.
tomwalters@0: 
tomwalters@0:     Decaying exponential:  A.exp(-t)    0<=t<=T
tomwalters@0:     Growing exponential:   A.exp(t)    -T<=t<=0
tomwalters@0: 	  or (shifting):   A.exp(t-T)   0<=t<=T
tomwalters@0: 
tomwalters@0:     To arrange for a decay factor to correspond to the half life, so that
tomwalters@0:     the wave grows/decays to half the given amplitude in the given decay time,
tomwalters@0:     the argument of the exponential must be calibrated to result in 0.5.
tomwalters@0:     If  exp(-x) = 0.5, then we have -x = ln(0.5) = -0.693147
tomwalters@0:     so that:  x = 0.693147
tomwalters@0:     For a given decay factor, the damped exponential decays to half the given
tomwalters@0:     amplitude in this time. The ramped exponential is a time-reversed damped
tomwalters@0:     exponential.
tomwalters@0: 
tomwalters@0: 
tomwalters@0: Examples:
tomwalters@0: 
tomwalters@0: 1. Growing exponentials
tomwalters@0: 
tomwalters@0: ramp polarity=ramp dec=1ms | x11plot
tomwalters@0: 
tomwalters@0: 2. Decaying exponentials
tomwalters@0: 
tomwalters@0: ramp polarity=damp dec=1ms | x11plot
tomwalters@0: 
tomwalters@0: 3. Half a cycle of an 8ms decaying exponential.
tomwalters@0: 
tomwalters@0: ramp polarity=damp dec=1ms dur=4ms | x11plot
tomwalters@0: 
tomwalters@0: 4. Modulating a tone with a damped exponential.
tomwalters@0: 
tomwalters@0: tone period=.5ms amp=500 type=float    > foo1
tomwalters@0: ramp pol=damp dec=1ms amp=1 type=float > foo2
tomwalters@0: merge op=mult type=float foo1 foo2  |  ftos | x11plot -n512
tomwalters@0: 
tomwalters@0: 5. Modulating a tone with a ramped exponential.
tomwalters@0: 
tomwalters@0: tone period=.5ms amp=500 type=float    > foo1
tomwalters@0: ramp pol=ramp dec=1ms amp=1 type=float > foo2
tomwalters@0: merge op=mult type=float foo1 foo2  |  ftos | x11plot -n512
tomwalters@0: 
tomwalters@0: 6. Modulating a tone with a damped exponential, and half-wave rectifying to
tomwalters@0:    generate damped pulses.
tomwalters@0: 
tomwalters@0: tone period=.5ms amp=500 type=float    > foo1
tomwalters@0: ramp pol=damp dec=1ms amp=1 type=float > foo2
tomwalters@0: merge op=mult type=float foo1 foo2 | ftos | gate range=min-0 op=0 | x11plot -n512
tomwalters@0: 
tomwalters@0: 7. Modulating white noise with a ramped exponential.
tomwalters@0: 
tomwalters@0: noise type=float  > foo1
tomwalters@0: ramp pol=ramp dec=1ms amp=1 type=float > foo2
tomwalters@0: merge op=mult type=float foo1 foo2 | ftos | x11plot -n512
tomwalters@0: 
tomwalters@0: 
tomwalters@0: */
tomwalters@0: 
tomwalters@0: #include <stdio.h>
tomwalters@0: #include <math.h>
tomwalters@0: #include "options.h"
tomwalters@0: #include "units.h"
tomwalters@0: #include "strmatch.h"
tomwalters@0: 
tomwalters@0: char applic[]  = "generate an exponential sawtooth waveform. " ;
tomwalters@0: char usage[]   = "ramp [options]" ;
tomwalters@0: 
tomwalters@0: static char *helpstr, *debugstr, *sampstr, *perstr, *astr, *decstr, *polstr, *dstr, *datastr ;
tomwalters@0: 
tomwalters@0: static Options option[] = {
tomwalters@0:     {   "help"      ,   "off"       ,  &helpstr     ,   "help"                     , DEBUG   },
tomwalters@0:     {   "debug"     ,   "off"       ,  &debugstr    ,   "debugging switch"         , DEBUG   },
tomwalters@0:     {   "samplerate",   "20kHz"     ,  &sampstr     ,   "samplerate "              , VAL     },
tomwalters@0:     {   "period"    ,   "8ms"       ,  &perstr      ,   "period [s,ms,p] of ramp"  , VAL     },
tomwalters@0:     {   "amplitude" ,   "1024"      ,  &astr        ,   "amplitude of waveform"    , VAL     },
tomwalters@0:     {   "decay"     ,   "2ms"       ,  &decstr      ,   "half-life of ramp"        , VAL     },
tomwalters@0:     {   "polarity"  ,   "ramp"      ,  &polstr      ,   "ramp (growing) / damp (decaying)", VAL },
tomwalters@0:     {   "duration"  ,   "500ms"     ,  &dstr        ,   "duration of waveform"     , VAL     },
tomwalters@0:     {   "type"      ,   "short"     ,  &datastr     ,   "o/p datatype (short/float)", VAL     },
tomwalters@0:    ( char * ) 0 } ;
tomwalters@0: 
tomwalters@0: 
tomwalters@0: #define DECAYFACTOR     ( 0.693147 )
tomwalters@0: 
tomwalters@0: int     samplerate ;
tomwalters@0: float   amplitude  ;
tomwalters@0: int     duration   ;
tomwalters@0: int     period     ;
tomwalters@0: int     decay      ;
tomwalters@0: double  decayrate  ;
tomwalters@0: 
tomwalters@0: main(argc, argv)
tomwalters@0: int   argc ;
tomwalters@0: char *argv[] ;
tomwalters@0: {
tomwalters@0:     int    i, n, t ;
tomwalters@0:     short  s ;
tomwalters@0:     float  f ;
tomwalters@0: 
tomwalters@0:     getopts( option,argc,argv ) ;
tomwalters@0:     if ( !isoff( helpstr ) )
tomwalters@0: 	helpopts3( helpstr, argv[0], applic, usage, option ) ;
tomwalters@0: 
tomwalters@0:     samplerate = to_Hz( sampstr, 0 ) ;
tomwalters@0:     amplitude  = atof( astr ) ;
tomwalters@0:     period     = (int)to_p( perstr, samplerate ) ;
tomwalters@0:     decay      = (int)to_p( decstr, samplerate ) ;
tomwalters@0:     duration   = to_p( dstr, samplerate )   ;
tomwalters@0: 
tomwalters@0: /*
tomwalters@0:     if ( decay >= period ) {
tomwalters@0: 	fprintf(stderr,"ramp: half-life period [%dp] must be less than waveform period [%dp]\n", decay, period);
tomwalters@0: 	exit( 1 ) ;
tomwalters@0:     }
tomwalters@0: */
tomwalters@0:     decayrate  = DECAYFACTOR / (double)decay ;
tomwalters@0: 
tomwalters@0:     if ( iststr( polstr, "damped" ) ) {
tomwalters@0: 
tomwalters@0: 	/* Decaying exponential */
tomwalters@0: 
tomwalters@0: 	if ( iststr( datastr, "short" ) )
tomwalters@0: 	    for ( i=0 ; i<duration ;  )
tomwalters@0: 		for ( t=0 ; t<period && i<duration ; t++, i++ ) {
tomwalters@0: 		    s = amplitude * exp( - (double)( t * decayrate ) ) ;
tomwalters@0: 		    fwrite( &s, sizeof(short), 1, stdout ) ;
tomwalters@0: 		}
tomwalters@0: 	else if ( iststr( datastr, "float" ) )
tomwalters@0: 	    for ( i=0 ; i<duration ;  )
tomwalters@0: 		for ( t=0 ; t<period && i<duration ; t++, i++ ) {
tomwalters@0: 		    f = amplitude * exp( - (double)( t * decayrate ) ) ;
tomwalters@0: 		    fwrite( &f, sizeof(float), 1, stdout ) ;
tomwalters@0: 		}
tomwalters@0: 	else
tomwalters@0: 	    fprintf(stderr,"unknown datatype [%s]\n", datastr) ;
tomwalters@0:     }
tomwalters@0:     else if ( iststr( polstr, "ramped" ) ) {
tomwalters@0: 
tomwalters@0: 	/* Growing exponential */
tomwalters@0: 
tomwalters@0: 	if ( iststr( datastr, "short" ) )
tomwalters@0: 	    for ( i=0 ; i<duration ;  )
tomwalters@0: 		for ( t=(-period) ; t<=0 && i<duration ; t++, i++ ) {
tomwalters@0: 		    s = amplitude * exp( (double)( t * decayrate ) ) ;
tomwalters@0: 		    fwrite( &s, sizeof(short), 1, stdout ) ;
tomwalters@0: 		}
tomwalters@0: 	else if ( iststr( datastr, "float" ) )
tomwalters@0: 	    for ( i=0 ; i<duration ;  )
tomwalters@0: 		for ( t=(-period) ; t<=0 && i<duration ; t++, i++ ) {
tomwalters@0: 		    f = amplitude * exp( (double)( t * decayrate ) ) ;
tomwalters@0: 		    fwrite( &f, sizeof(float), 1, stdout ) ;
tomwalters@0: 		}
tomwalters@0: 	else
tomwalters@0: 	    fprintf(stderr,"unknown datatype [%s]\n", datastr) ;
tomwalters@0:     }
tomwalters@0:     else
tomwalters@0: 	fprintf( stderr, "unknown polarity [%s]\n", polstr ) ;
tomwalters@0: }