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adsr: Fix attack envelope.

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This commit is contained in:
Stuart Longland 2017-04-08 21:41:02 +10:00
parent b77e364f53
commit ba94adbfd1
Signed by: stuartl
GPG Key ID: F954BBBB7948D546
1 changed files with 22 additions and 19 deletions
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41
adsr.c
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@ -26,25 +26,24 @@
#endif
/* ADSR attack/decay adjustments */
#define ADSR_EXP_AMP_FACTOR (6)
#define ADSR_EXP_SHIFT (-8)
#define ADSR_EXP_TIME_FACTOR (1)
#define ADSR_LIN_AMP_FACTOR (6)
#define ADSR_DECAY_OFFSET (16)
/*!
* ADSR Attack amplitude exponential shift.
*/
static uint8_t adsr_attack_shift(uint8_t sample) {
return (sample + ADSR_EXP_SHIFT)/ADSR_EXP_TIME_FACTOR
- ADSR_EXP_AMP_FACTOR;
static uint8_t adsr_attack_amp(uint8_t amp, uint8_t count) {
if (count >= 8)
return 0;
amp >>= count;
return amp;
}
/*!
* ADSR Release amplitude exponential shift.
*/
static uint8_t adsr_release_shift(uint8_t sample) {
return adsr_attack_shift(ADSR_DECAY_OFFSET - sample);
static uint8_t adsr_release_amp(uint8_t amp, uint8_t count) {
return adsr_attack_amp(amp, 16 - count);
}
/*!
@ -127,27 +126,31 @@ uint8_t adsr_next(struct adsr_env_gen_t* const adsr) {
}
if (adsr->state == ADSR_STATE_ATTACK_INIT) {
_DPRINTF("adsr=%p ATTACK INIT\n", adsr);
/* Attack is divided into 16 segments */
adsr->time_step = (uint16_t)((adsr->attack_time
* adsr->time_scale) >> 4);
adsr->counter = 16;
adsr->next_event = adsr->time_step;
adsr->state = ADSR_STATE_ATTACK;
_DPRINTF("adsr=%p ATTACK INIT tstep=%d\n",
adsr, adsr->time_step);
}
if (adsr->state == ADSR_STATE_ATTACK) {
_DPRINTF("adsr=%p ATTACK\n", adsr);
_DPRINTF("adsr=%p ATTACK count=%d\n", adsr,
adsr->counter);
if (adsr->counter) {
/* Change of amplitude */
uint16_t lin_amp = (16-adsr->counter)
* adsr->peak_amp;
adsr->amplitude = lin_amp
>> ADSR_LIN_AMP_FACTOR;
adsr->amplitude += adsr->peak_amp >>
adsr_attack_shift(adsr->counter);
uint16_t exp_amp = adsr_attack_amp(
adsr->peak_amp, adsr->counter);
lin_amp >>= ADSR_LIN_AMP_FACTOR;
_DPRINTF("adsr=%p ATTACK lin=%d exp=%d\n",
adsr, lin_amp, exp_amp);
adsr->amplitude = lin_amp + exp_amp;
/* Go around again */
adsr->counter--;
adsr->next_event = adsr->time_step;
@ -245,8 +248,8 @@ uint8_t adsr_next(struct adsr_env_gen_t* const adsr) {
* adsr->peak_amp;
adsr->amplitude = lin_amp
>> ADSR_LIN_AMP_FACTOR;
adsr->amplitude += adsr->peak_amp >>
adsr_release_shift(adsr->counter);
adsr->amplitude += adsr_release_amp(
adsr->sustain_amp, adsr->counter);
/* Go around again */
adsr->counter--;
adsr->next_event = adsr->time_step;
@ -259,7 +262,7 @@ uint8_t adsr_next(struct adsr_env_gen_t* const adsr) {
_DPRINTF("adsr=%p RELEASE EXPIRE\n", adsr);
/* Reset the state */
adsr->state = ADSR_STATE_IDLE;
adsr->state = ADSR_STATE_DONE;
adsr->amplitude = 0;
}