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Implement first-order feedback audio filter

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This commit is contained in:
Nikita Lisitsa 2023-10-03 14:32:31 +03:00
parent 9cbb9127b9
commit 9a800b8f7a
2 changed files with 50 additions and 1 deletions
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5
libs/audio/include/psemek/audio/effect/filter.hpp
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@ -5,9 +5,12 @@
namespace psemek::audio
{
// Turns x[n] into a0*x[n] + a1*x[n-1]
// Turns x[n] into y[n] = a0*x[n] + a1*x[n-1]
stream_ptr feedforward_filter(stream_ptr stream, float a0, float a1);
// Turns x[n] into y[n] = a0*x[n] + b1*y[n-1]
stream_ptr feedback_filter(stream_ptr stream, float a0, float b1);
stream_ptr low_pass_filter(stream_ptr stream);
stream_ptr high_pass_filter(stream_ptr stream);

46
libs/audio/source/effect/filter.cpp
View file

@ -48,6 +48,47 @@ namespace psemek::audio
float prev_[2]{0.f};
};
struct feedback_filter_impl
: stream
{
feedback_filter_impl(stream_ptr stream, float a0, float b1)
: stream_(std::move(stream))
, a0_(a0)
, b1_(b1)
{}
std::optional<std::size_t> length() const override
{
return stream_->length();
}
std::size_t read(util::span<float> samples) override
{
std::size_t count = stream_->read(samples);
for (std::size_t i = 0; i < count; i += 2)
{
samples[i + 0] = prev_[0] * b1_ + samples[i + 0] * a0_;
samples[i + 1] = prev_[1] * b1_ + samples[i + 1] * a0_;
prev_[0] = samples[i + 0];
prev_[1] = samples[i + 1];
}
return count;
}
std::size_t played() const override
{
return stream_->played();
}
private:
stream_ptr stream_;
float a0_;
float b1_;
float prev_[2]{0.f};
};
}
stream_ptr feedforward_filter(stream_ptr stream, float a0, float a1)
@ -55,6 +96,11 @@ namespace psemek::audio
return std::make_shared<feedforward_filter_impl>(std::move(stream), a0, a1);
}
stream_ptr feedback_filter(stream_ptr stream, float a0, float b1)
{
return std::make_shared<feedback_filter_impl>(std::move(stream), a0, b1);
}
stream_ptr low_pass_filter(stream_ptr stream)
{
return feedforward_filter(std::move(stream), 1.f, 1.f);