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Merge pull request #444 from TomHarte/AppleAudio

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Introduces a low-pass filter for the Apple II
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Thomas Harte 2018-05-15 21:33:52 -04:00 committed by GitHub
commit bfdd3468ea
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2 changed files with 23 additions and 20 deletions
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5
Machines/AppleII/AppleII.cpp
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@ -139,6 +139,11 @@ class ConcreteMachine:
// decision to sample it at seven times the CPU clock (plus stretches).
speaker_.set_input_rate(static_cast<float>(master_clock / (2.0 * static_cast<float>(audio_divider))));
// Apply a 6Khz low-pass filter. This was picked by ear and by an attempt to understand the
// Apple II schematic but, well, I don't claim much insight on the latter. This is definitely
// something to review in the future.
speaker_.set_high_frequency_cutoff(6000);
// Also, start with randomised memory contents.
Memory::Fuzz(ram_, sizeof(ram_));
}

38
OSBindings/Mac/Clock Signal/Audio/CSAudioQueue.m
View File

@ -27,9 +27,9 @@ static NSLock *CSAudioQueueDeallocLock;
@implementation CSAudioQueue {
AudioQueueRef _audioQueue;
AudioQueueBufferRef _storedBuffers[NumberOfStoredAudioQueueBuffer];
NSLock *_storedBuffersLock;
CSWeakAudioQueuePointer *_weakPointer;
int _enqueuedBuffers;
}
#pragma mark - AudioQueue callbacks
@ -39,16 +39,19 @@ static NSLock *CSAudioQueueDeallocLock;
*/
- (BOOL)audioQueue:(AudioQueueRef)theAudioQueue didCallbackWithBuffer:(AudioQueueBufferRef)buffer {
[_storedBuffersLock lock];
for(int c = 0; c < NumberOfStoredAudioQueueBuffer; c++) {
if(!_storedBuffers[c] || buffer->mAudioDataBytesCapacity > _storedBuffers[c]->mAudioDataBytesCapacity) {
if(_storedBuffers[c]) AudioQueueFreeBuffer(_audioQueue, _storedBuffers[c]);
_storedBuffers[c] = buffer;
[_storedBuffersLock unlock];
return YES;
}
--_enqueuedBuffers;
// If that leaves nothing in the queue, re-enqueue whatever just came back in order to keep the
// queue going. AudioQueues seem to stop playing and never restart no matter how much encouragement
// if exhausted.
if(!_enqueuedBuffers) {
AudioQueueEnqueueBuffer(theAudioQueue, buffer, 0, NULL);
++_enqueuedBuffers;
} else {
AudioQueueFreeBuffer(_audioQueue, buffer);
}
[_storedBuffersLock unlock];
AudioQueueFreeBuffer(_audioQueue, buffer);
return YES;
}
@ -158,18 +161,12 @@ static void audioOutputCallback(
size_t bufferBytes = lengthInSamples * sizeof(int16_t);
[_storedBuffersLock lock];
for(int c = 0; c < NumberOfStoredAudioQueueBuffer; c++) {
if(_storedBuffers[c] && _storedBuffers[c]->mAudioDataBytesCapacity >= bufferBytes) {
memcpy(_storedBuffers[c]->mAudioData, buffer, bufferBytes);
_storedBuffers[c]->mAudioDataByteSize = (UInt32)bufferBytes;
AudioQueueEnqueueBuffer(_audioQueue, _storedBuffers[c], 0, NULL);
_storedBuffers[c] = NULL;
[_storedBuffersLock unlock];
return;
}
// Don't enqueue more than 4 buffers ahead of now, to ensure not too much latency accrues.
if(_enqueuedBuffers > 4) {
[_storedBuffersLock unlock];
return;
}
[_storedBuffersLock unlock];
++_enqueuedBuffers;
AudioQueueBufferRef newBuffer;
AudioQueueAllocateBuffer(_audioQueue, (UInt32)bufferBytes * 2, &newBuffer);
@ -177,6 +174,7 @@ static void audioOutputCallback(
newBuffer->mAudioDataByteSize = (UInt32)bufferBytes;
AudioQueueEnqueueBuffer(_audioQueue, newBuffer, 0, NULL);
[_storedBuffersLock unlock];
}
#pragma mark - Sampling Rate getters