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Diffstat (limited to 'libsidplay2/sidplay-libs-2.1.0/resid/extfilt.h')
| -rw-r--r-- | libsidplay2/sidplay-libs-2.1.0/resid/extfilt.h | 169 |
1 files changed, 0 insertions, 169 deletions
diff --git a/libsidplay2/sidplay-libs-2.1.0/resid/extfilt.h b/libsidplay2/sidplay-libs-2.1.0/resid/extfilt.h deleted file mode 100644 index 84c204ef..00000000 --- a/libsidplay2/sidplay-libs-2.1.0/resid/extfilt.h +++ /dev/null @@ -1,169 +0,0 @@ -// --------------------------------------------------------------------------- -// This file is part of reSID, a MOS6581 SID emulator engine. -// Copyright (C) 2002 Dag Lem <resid@nimrod.no> -// -// This program is free software; you can redistribute it and/or modify -// it under the terms of the GNU General Public License as published by -// the Free Software Foundation; either version 2 of the License, or -// (at your option) any later version. -// -// This program is distributed in the hope that it will be useful, -// but WITHOUT ANY WARRANTY; without even the implied warranty of -// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -// GNU General Public License for more details. -// -// You should have received a copy of the GNU General Public License -// along with this program; if not, write to the Free Software -// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA -// --------------------------------------------------------------------------- - -#ifndef __EXTFILT_H__ -#define __EXTFILT_H__ - -#include "siddefs.h" - -RESID_NAMESPACE_START - -// ---------------------------------------------------------------------------- -// The audio output stage in a Commodore 64 consists of two STC networks, -// a low-pass filter with 3-dB frequency 16kHz followed by a high-pass -// filter with 3-dB frequency 16Hz (the latter provided an audio equipment -// input impedance of 1kOhm). -// The STC networks are connected with a BJT supposedly meant to act as -// a unity gain buffer, which is not really how it works. A more elaborate -// model would include the BJT, however DC circuit analysis yields BJT -// base-emitter and emitter-base impedances sufficiently low to produce -// additional low-pass and high-pass 3dB-frequencies in the order of hundreds -// of kHz. This calls for a sampling frequency of several MHz, which is far -// too high for practical use. -// ---------------------------------------------------------------------------- -class ExternalFilter -{ -public: - ExternalFilter(); - - void enable_filter(bool enable); - void set_sampling_parameter(double pass_freq); - void set_chip_model(chip_model model); - - RESID_INLINE void clock(sound_sample Vi); - RESID_INLINE void clock(cycle_count delta_t, sound_sample Vi); - void reset(); - - // Audio output (20 bits). - RESID_INLINE sound_sample output(); - -protected: - // Filter enabled. - bool enabled; - - // Maximum mixer DC offset. - sound_sample mixer_DC; - - // State of filters. - sound_sample Vlp; // lowpass - sound_sample Vhp; // highpass - sound_sample Vo; - - // Cutoff frequencies. - sound_sample w0lp; - sound_sample w0hp; - -friend class SID; -}; - - -// ---------------------------------------------------------------------------- -// Inline functions. -// The following functions are defined inline because they are called every -// time a sample is calculated. -// ---------------------------------------------------------------------------- - -#if RESID_INLINING || defined(__EXTFILT_CC__) - -// ---------------------------------------------------------------------------- -// SID clocking - 1 cycle. -// ---------------------------------------------------------------------------- -RESID_INLINE -void ExternalFilter::clock(sound_sample Vi) -{ - // This is handy for testing. - if (!enabled) { - // Remove maximum DC level since there is no filter to do it. - Vlp = Vhp = 0; - Vo = Vi - mixer_DC; - return; - } - - // delta_t is converted to seconds given a 1MHz clock by dividing - // with 1 000 000. - - // Calculate filter outputs. - // Vo = Vlp - Vhp; - // Vlp = Vlp + w0lp*(Vi - Vlp)*delta_t; - // Vhp = Vhp + w0hp*(Vlp - Vhp)*delta_t; - - sound_sample dVlp = (w0lp >> 8)*(Vi - Vlp) >> 12; - sound_sample dVhp = w0hp*(Vlp - Vhp) >> 20; - Vo = Vlp - Vhp; - Vlp += dVlp; - Vhp += dVhp; -} - -// ---------------------------------------------------------------------------- -// SID clocking - delta_t cycles. -// ---------------------------------------------------------------------------- -RESID_INLINE -void ExternalFilter::clock(cycle_count delta_t, - sound_sample Vi) -{ - // This is handy for testing. - if (!enabled) { - // Remove maximum DC level since there is no filter to do it. - Vlp = Vhp = 0; - Vo = Vi - mixer_DC; - return; - } - - // Maximum delta cycles for the external filter to work satisfactorily - // is approximately 8. - cycle_count delta_t_flt = 8; - - while (delta_t) { - if (delta_t < delta_t_flt) { - delta_t_flt = delta_t; - } - - // delta_t is converted to seconds given a 1MHz clock by dividing - // with 1 000 000. - - // Calculate filter outputs. - // Vo = Vlp - Vhp; - // Vlp = Vlp + w0lp*(Vi - Vlp)*delta_t; - // Vhp = Vhp + w0hp*(Vlp - Vhp)*delta_t; - - sound_sample dVlp = (w0lp*delta_t_flt >> 8)*(Vi - Vlp) >> 12; - sound_sample dVhp = w0hp*delta_t_flt*(Vlp - Vhp) >> 20; - Vo = Vlp - Vhp; - Vlp += dVlp; - Vhp += dVhp; - - delta_t -= delta_t_flt; - } -} - - -// ---------------------------------------------------------------------------- -// Audio output (19.5 bits). -// ---------------------------------------------------------------------------- -RESID_INLINE -sound_sample ExternalFilter::output() -{ - return Vo; -} - -#endif // RESID_INLINING || defined(__EXTFILT_CC__) - -RESID_NAMESPACE_STOP - -#endif // not __EXTFILT_H__ |