reSIDfp::ExternalFilter Class Reference

#include <ExternalFilter.h>

Public Member Functions
int32_t	clock (int32_t input)
	ExternalFilter ()
void	setClockFrequency (double frequency)
void	setExtResistance (double res)
void	reset ()

Friends
class	State

Detailed Description

The audio output stage in a Commodore 64 consists of two STC networks, a low-pass RC filter with 3 dB frequency 16kHz followed by a DC-blocker which acts as a high-pass filter with a cutoff dependent on the attached audio equipment impedance. Here we suppose an impedance of 10kOhm resulting in a 3 dB attenuation at 1.6Hz. The STC networks are connected with a BJT based common collector used as a voltage follower (featuring a 2SC1815 NPN transistor).

To operate properly the 6581 audio output needs a pull-down resistor, 1KOhm is the recommended value.

• ~~~ 9/12V --—+ audio| 10k | +—o-—R—o-----—o--—(K) +--— out | | | | | |audio --—+ R 1k C 1000 | | 10 uF | | | pF +-C-—o--—C--—+ ~10k 470 | | GND GND pF R 1K | amp
  • ** | +--—

    GND
    

• ~~~

  • Pulldown resistor, only for the 6581. ** The C64c board additionally includes a bootstrap capacitor to increase the input impedance of the common collector.

  The C128 boards include an additional capacitor and a resistor to the ouptput stage.

• ~~~ 9/12V --—+ audio| 10k | +—o-—R—o-----—o--—(K) +--— out | | | | | |audio --—+ R 1k C 1000 | | 10 uF | | | pF +-C-—o--—o-—C—o---—+ ~10k 470 | | | | GND GND pF R 1K C 220pF R 47K | amp

  • | | | +--—

    GND GND GND

• ~~~

Constructor & Destructor Documentation

reSIDfp::ExternalFilter::ExternalFilter

(

)

Constructor.

Member Function Documentation

RESIDFP_INLINE int32_t reSIDfp::ExternalFilter::clock

(

int32_t

input

)

SID clocking.

Parameters

input

input sample, signed 16 bit

Returns

filtered sample, signed 16 bit

void reSIDfp::ExternalFilter::reset

(

)

SID reset.

void reSIDfp::ExternalFilter::setClockFrequency

(

double

frequency

)

Setup of the external filter sampling parameters.

Parameters

frequency

the main system clock frequency in Hertz

void reSIDfp::ExternalFilter::setExtResistance

(

double

res

)

Setup of the external filter sampling parameters.

Parameters

res	the resistance value in Ohms

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The documentation for this class was generated from the following files:

• ExternalFilter.h
• ExternalFilter.cpp