Apple-2-Tools/bradgrantham-apple2e
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Slightly better audio using a sine wave approximation

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Choose a 2000Hz sine wave as a trade off between smoothing audio and preserving audio

Fix #14
This commit is contained in:
Brad Grantham 2016-12-06 18:24:11 -08:00
parent f7b76a8631
commit 1d8a138123
1 changed files with 32 additions and 4 deletions
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36
apple2e.cpp
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@ -1,4 +1,5 @@
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <set>
@ -450,6 +451,21 @@ struct DISKIIboard : board_base
virtual void reset(void) {}
};
const int waveform_length = 44100 / 500 / 2; // half of a wave at 4000 Hz
const float waveform_max_amplitude = .35f;
static unsigned char waveform[waveform_length];
static void initialize_audio_waveform() __attribute__((constructor));
void initialize_audio_waveform()
{
for(int i = 0; i < waveform_length; i++) {
float theta = (float(i) / (waveform_length - 1) -.5f) * M_PI;
waveform[i] = 127.5 + waveform_max_amplitude * 127.5 * sin(theta);
printf("%d: %d\n", i, waveform[i]);
}
}
struct MAINboard : board_base
{
system_clock& clk;
@ -551,13 +567,22 @@ struct MAINboard : board_base
char audio_buffer[audio_buffer_size];
long long audio_buffer_start_sample = 0;
long long audio_buffer_next_sample = -1;
bool speaker_energized = false;
unsigned char speaker_level;
bool speaker_transitioning_to_high = false;
int where_in_waveform = 0;
void fill_flush_audio()
{
long long current_sample = clk * sample_rate / machine_clock_rate;
for(long long i = audio_buffer_next_sample; i < current_sample; i++) {
audio_buffer[i % audio_buffer_size] = speaker_energized ? 128 - 32 : 128 + 32;
if(where_in_waveform < waveform_length) {
unsigned char level = waveform[where_in_waveform++];
speaker_level = speaker_transitioning_to_high ? level : (255 - level);
}
audio_buffer[i % audio_buffer_size] = speaker_level;
if(i - audio_buffer_start_sample == audio_buffer_size - 1) {
audio_flush(audio_buffer, audio_buffer_size);
@ -594,6 +619,7 @@ struct MAINboard : board_base
MAINboard(system_clock& clk_, unsigned char rom_image[32768], display_write_func display_write_, audio_flush_func audio_flush_, get_paddle_func get_paddle_) :
clk(clk_),
internal_C800_ROM_selected(true),
speaker_level(waveform[0]),
display_write(display_write_),
audio_flush(audio_flush_),
get_paddle(get_paddle_)
@ -711,7 +737,8 @@ struct MAINboard : board_base
fill_flush_audio();
data = 0x00;
speaker_energized = !speaker_energized;
where_in_waveform = 0;
speaker_transitioning_to_high = !speaker_transitioning_to_high;
return true;
} else if(addr == 0xC010) {
// reset keyboard latch
@ -846,7 +873,8 @@ struct MAINboard : board_base
if(debug & DEBUG_RW) printf("write SPKR\n");
fill_flush_audio();
data = 0x00;
speaker_energized = !speaker_energized;
where_in_waveform = 0;
speaker_transitioning_to_high = !speaker_transitioning_to_high;
return true;
}
printf("unhandled MMIO Write at %04X\n", addr);