// license:BSD-3-Clause // copyright-holders:Derrick Renaud, Couriersud #include "emu.h" #include "flt_rc.h" // device type definition DEFINE_DEVICE_TYPE(FILTER_RC, filter_rc_device, "filter_rc", "RC Filter") //************************************************************************** // LIVE DEVICE //************************************************************************** //------------------------------------------------- // filter_rc_device - constructor //------------------------------------------------- filter_rc_device::filter_rc_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock) : device_t(mconfig, FILTER_RC, tag, owner, clock), device_sound_interface(mconfig, *this), m_stream(nullptr), m_k(0), m_memory(0), m_type(LOWPASS), m_R1(1), m_R2(1), m_R3(1), m_C(0) { } //------------------------------------------------- // device_start - device-specific startup //------------------------------------------------- void filter_rc_device::device_start() { m_stream = stream_alloc(1, 1, machine().sample_rate()); recalc(); save_item(NAME(m_k)); save_item(NAME(m_memory)); save_item(NAME(m_type)); save_item(NAME(m_R1)); save_item(NAME(m_R2)); save_item(NAME(m_R3)); save_item(NAME(m_C)); } //------------------------------------------------- // sound_stream_update - handle a stream update //------------------------------------------------- void filter_rc_device::sound_stream_update(sound_stream &stream, stream_sample_t **inputs, stream_sample_t **outputs, int samples) { stream_sample_t *src = inputs[0]; stream_sample_t *dst = outputs[0]; int memory = m_memory; switch (m_type) { case LOWPASS: while (samples--) { memory += ((*src++ - memory) * m_k) / 0x10000; *dst++ = memory; } break; case HIGHPASS: case AC: while (samples--) { *dst++ = *src - memory; memory += ((*src++ - memory) * m_k) / 0x10000; } break; } m_memory = memory; } void filter_rc_device::recalc() { double Req; switch (m_type) { case LOWPASS: if (m_C == 0.0) { /* filter disabled */ m_k = 0x10000; return; } Req = (m_R1 * (m_R2 + m_R3)) / (m_R1 + m_R2 + m_R3); break; case HIGHPASS: case AC: if (m_C == 0.0) { /* filter disabled */ m_k = 0x0; m_memory = 0x0; return; } Req = m_R1; break; default: fatalerror("filter_rc_setRC: Wrong filter type %d\n", m_type); } /* Cut Frequency = 1/(2*Pi*Req*C) */ /* k = (1-(EXP(-TIMEDELTA/RC))) */ m_k = 0x10000 - 0x10000 * (exp(-1 / (Req * m_C) / machine().sample_rate())); }