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Ensures no input data is dropped when changing output rates.

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I think this 'completely' deals with the problem. At least until someone wants dynamic output buffer sizes or something like that. We'll see.
This commit is contained in:
Thomas Harte 2020-02-09 19:14:25 -05:00
parent b04daca98e
commit 6bda4034c6
1 changed files with 92 additions and 54 deletions
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118
Outputs/Speaker/Implementation/LowpassSpeaker.hpp
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@ -109,6 +109,12 @@ template <typename T> class LowpassSpeaker: public Speaker {
}
private:
enum class Conversion {
ResampleSmaller,
Copy,
ResampleLarger
} conversion_ = Conversion::Copy;
/*!
Advances by the number of cycles specified, obtaining data from the sample source supplied
at construction, filtering it and passing it on to the speaker's delegate if there is one.
@ -131,10 +137,8 @@ template <typename T> class LowpassSpeaker: public Speaker {
delegate_->speaker_did_change_input_clock(this);
}
// If input and output rates exactly match, and no additional cut-off has been specified,
// just accumulate results and pass on.
if( filter_parameters.input_cycles_per_second == filter_parameters.output_cycles_per_second &&
filter_parameters.high_frequency_cutoff < 0.0) {
switch(conversion_) {
case Conversion::Copy:
while(cycles_remaining) {
const auto cycles_to_read = std::min(output_buffer_.size() - output_buffer_pointer_, cycles_remaining);
@ -149,13 +153,9 @@ template <typename T> class LowpassSpeaker: public Speaker {
cycles_remaining -= cycles_to_read;
}
break;
return;
}
// If the output rate is less than the input rate, or an additional cut-off has been specified, use the filter.
if( filter_parameters.input_cycles_per_second > filter_parameters.output_cycles_per_second ||
(filter_parameters.input_cycles_per_second == filter_parameters.output_cycles_per_second && filter_parameters.high_frequency_cutoff >= 0.0)) {
case Conversion::ResampleSmaller:
while(cycles_remaining) {
const auto cycles_to_read = std::min(cycles_remaining, input_buffer_.size() - input_buffer_depth_);
sample_source_.get_samples(cycles_to_read, &input_buffer_[input_buffer_depth_]);
@ -163,37 +163,15 @@ template <typename T> class LowpassSpeaker: public Speaker {
input_buffer_depth_ += cycles_to_read;
if(input_buffer_depth_ == input_buffer_.size()) {
output_buffer_[output_buffer_pointer_] = filter_->apply(input_buffer_.data());
output_buffer_pointer_++;
resample_input_buffer();
}
}
break;
// Announce to delegate if full.
if(output_buffer_pointer_ == output_buffer_.size()) {
output_buffer_pointer_ = 0;
did_complete_samples(this, output_buffer_);
case Conversion::ResampleLarger:
// TODO: input rate is less than output rate.
break;
}
// If the next loop around is going to reuse some of the samples just collected, use a memmove to
// preserve them in the correct locations (TODO: use a longer buffer to fix that) and don't skip
// anything. Otherwise skip as required to get to the next sample batch and don't expect to reuse.
const auto steps = stepper_->step();
if(steps < input_buffer_.size()) {
auto *const input_buffer = input_buffer_.data();
std::memmove( input_buffer,
&input_buffer[steps],
sizeof(int16_t) * (input_buffer_.size() - steps));
input_buffer_depth_ -= steps;
} else {
if(steps > input_buffer_.size())
sample_source_.skip_samples(steps - input_buffer_.size());
input_buffer_depth_ = 0;
}
}
}
return;
}
// TODO: input rate is less than output rate
}
T &sample_source_;
@ -239,9 +217,69 @@ template <typename T> class LowpassSpeaker: public Speaker {
high_pass_frequency,
SignalProcessing::FIRFilter::DefaultAttenuation);
input_buffer_.resize(std::size_t(number_of_taps));
// Pick the new conversion function.
if( filter_parameters.input_cycles_per_second == filter_parameters.output_cycles_per_second &&
filter_parameters.high_frequency_cutoff < 0.0) {
// If input and output rates exactly match, and no additional cut-off has been specified,
// just accumulate results and pass on.
conversion_ = Conversion::Copy;
} else if( filter_parameters.input_cycles_per_second > filter_parameters.output_cycles_per_second ||
(filter_parameters.input_cycles_per_second == filter_parameters.output_cycles_per_second && filter_parameters.high_frequency_cutoff >= 0.0)) {
// If the output rate is less than the input rate, or an additional cut-off has been specified, use the filter.
conversion_ = Conversion::ResampleSmaller;
} else {
conversion_ = Conversion::ResampleLarger;
}
// Do something sensible with any dangling input, if necessary.
switch(conversion_) {
// Neither direct copying nor resampling larger currently use any temporary input.
// Although in the latter case that's just because it's unimplemented. But, regardless,
// that means nothing to do.
default: break;
case Conversion::ResampleSmaller:
// Reize the input buffer only if absolutely necessary; if sizing downward
// such that a sample would otherwise be lost then output it now. Keep anything
// currently in the input buffer that hasn't yet been processed.
if(input_buffer_.size() != size_t(number_of_taps)) {
if(input_buffer_depth_ >= size_t(number_of_taps)) {
resample_input_buffer();
input_buffer_depth_ %= size_t(number_of_taps);
}
input_buffer_.resize(size_t(number_of_taps));
}
break;
}
}
inline void resample_input_buffer() {
output_buffer_[output_buffer_pointer_] = filter_->apply(input_buffer_.data());
output_buffer_pointer_++;
// Announce to delegate if full.
if(output_buffer_pointer_ == output_buffer_.size()) {
output_buffer_pointer_ = 0;
did_complete_samples(this, output_buffer_);
}
// If the next loop around is going to reuse some of the samples just collected, use a memmove to
// preserve them in the correct locations (TODO: use a longer buffer to fix that?) and don't skip
// anything. Otherwise skip as required to get to the next sample batch and don't expect to reuse.
const auto steps = stepper_->step();
if(steps < input_buffer_.size()) {
auto *const input_buffer = input_buffer_.data();
std::memmove( input_buffer,
&input_buffer[steps],
sizeof(int16_t) * (input_buffer_.size() - steps));
input_buffer_depth_ -= steps;
} else {
if(steps > input_buffer_.size())
sample_source_.skip_samples(steps - input_buffer_.size());
input_buffer_depth_ = 0;
}
}
};
}