de.quippy.sidplay.resid_builder.resid

Class ExternalFilter

java.lang.Object

de.quippy.sidplay.resid_builder.resid.ExternalFilter

public class ExternalFilter
extends Object

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.

Author:

Ken Händel

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	enabled Filter enabled.
protected int	mixer_DC Maximum mixer DC offset.
protected int	vhp State of filters. highpass
protected int	vlp State of filters. lowpass
protected int	vo State of filters.
protected int	w0hp Cutoff frequencies.
protected int	w0lp Cutoff frequencies.

Constructor Summary

Constructors

Constructor and Description
ExternalFilter() Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
void	clock(int Vi) SID clocking - 1 cycle.
void	clock(int delta_t, int Vi) SID clocking - delta_t cycles.
void	enable_filter(boolean enable) Enable filter.
int	output() Audio output (20 bits).
void	reset() SID reset.
void	set_chip_model(ISIDDefs.chip_model model) Set chip model.
void	set_sampling_parameter(double pass_freq) Setup of the external filter sampling parameters.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

enabled

protected boolean enabled

Filter enabled.

mixer_DC

protected int mixer_DC

Maximum mixer DC offset.

vlp

protected int vlp

State of filters. lowpass

vhp

protected int vhp

State of filters. highpass

vo

protected int vo

State of filters.

w0lp

protected int w0lp

Cutoff frequencies.

w0hp

protected int w0hp

Cutoff frequencies.

Constructor Detail

ExternalFilter

public ExternalFilter()

Constructor.

Method Detail

clock

public void clock(int Vi)

SID clocking - 1 cycle.

Parameters:

Vi -

clock

public void clock(int delta_t,
         int Vi)

SID clocking - delta_t cycles.

Parameters:

delta_t -

Vi -

output

public int output()

Audio output (20 bits). Audio output (19.5 bits).

Returns:

vo

enable_filter

public void enable_filter(boolean enable)

Enable filter.

Parameters:

enable - enable filter

set_sampling_parameter

public void set_sampling_parameter(double pass_freq)

Setup of the external filter sampling parameters.

Parameters:

pass_freq -

set_chip_model

public void set_chip_model(ISIDDefs.chip_model model)

Set chip model.

Parameters:

model - chip model

reset

public void reset()

SID reset.