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Use formula derived from figures 2 and 3 in LS624 datasheet. Coefficients

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where calculated using least square approximation.
This approach gives a bit better audible results compared to the prior approach.
This commit is contained in:
Couriersud 2009-01-25 02:10:31 +00:00
parent 2c9f0e33fb
commit 84683a2e5b
1 changed files with 12 additions and 6 deletions
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18
src/emu/sound/disc_dev.c
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@ -1582,13 +1582,19 @@ static DISCRETE_RESET(dsd_566)
#define DSD_LS624__OUTTYPE (*(node->input[4]))
/*
* These formulas are derived from diagrams in the datasheet!
* They are not based on any law. The function is not
* described anywhere.
* The datasheet mentions a 600 ohm discharge. It also gives
* equivalent circuits for VI and VR.
*/
#define LS624_F1(x) (0.19 + 20.0/90.0*(x))
#define LS624_T(_C, _R, _F) (-600.0 * (_C) * log(1.0-LS624_F1(_R)*0.12/LS624_F1(_F)))
#define LS624_T(_C, _R, _F) ((-600.0 * (_C) * log(1.0-LS624_F1(_R)*0.12/LS624_F1(_F))) * 16.0 )
/* The following formula was derived from figures 2 and 3 in LS624 datasheet. Coefficients
* where calculated using least square approximation.
* This approach gives a bit better results compared to the first approach.
*/
#define LS624_F(_C, _VI, _VR) pow(10, -0.912029404 * log10(_C) + 0.243264328 * (_VI) \
- 0.091695877 * (_VR) -0.014110946 * (_VI) * (_VR) - 3.207072925)
static DISCRETE_STEP(dsd_ls624)
{
@ -1602,8 +1608,8 @@ static DISCRETE_STEP(dsd_ls624)
int lst, cntf = 0, cntr = 0;
sample_t = discrete_current_context->sample_time; /* Change in time */
dt = LS624_T(DSD_LS624__C, DSD_LS624__VRNG, DSD_LS624__VMOD);
dt = 16 * dt;
//dt = LS624_T(DSD_LS624__C, DSD_LS624__VRNG, DSD_LS624__VMOD) / 2.0;
dt = 1.0f / (2.0f * LS624_F(DSD_LS624__C, DSD_LS624__VMOD, DSD_LS624__VRNG));
t = context->remain;
lst = context->state;
while (t + dt < sample_t)