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SoundPlayer: Use overlapping windows for bars visualization

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For DSP reasons I can't explain myself (yet, sorry), short-time Fourier
transform (STFT) is much more accurate and aesthetically pleasing when
the windows that select the samples for STFT overlap. This implements
that behavior by storing the previous samples and performing windowed
FFT over both it as well as the current samples. This gives us 50%
overlap between windows, a common standard that is nice to look at.
This commit is contained in:
kleines Filmröllchen 2022-03-03 22:32:45 +01:00 • committed by Andreas Kling
parent a5d95aa6e8
commit 21266f42f1
2 changed files with 13 additions and 4 deletions
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14
Userland/Applications/SoundPlayer/BarsVisualizationWidget.cpp
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@ -7,6 +7,7 @@
#include "BarsVisualizationWidget.h"
#include <AK/Math.h>
#include <AK/TypedTransfer.h>
#include <LibDSP/FFT.h>
#include <LibDSP/Window.h>
#include <LibGUI/Event.h>
@ -22,8 +23,14 @@ void BarsVisualizationWidget::render(GUI::PaintEvent& event, FixedArray<double>
painter.add_clip_rect(event.rect());
painter.fill_rect(frame_inner_rect(), Color::Black);
for (size_t i = 0; i < fft_size; i++)
m_fft_samples[i] = samples[i] * m_fft_window[i];
// First half of data is from previous iteration, second half is from now.
// This gives us fully overlapping windows, which result in more accurate and visually appealing STFT.
for (size_t i = 0; i < fft_size / 2; i++)
m_fft_samples[i] = m_previous_samples[i] * m_fft_window[i];
for (size_t i = 0; i < fft_size / 2; i++)
m_fft_samples[i + fft_size / 2] = samples[i] * m_fft_window[i + fft_size / 2];
AK::TypedTransfer<double>::copy(m_previous_samples.data(), samples.data(), samples.size());
LibDSP::fft(m_fft_samples.span(), false);
@ -74,7 +81,8 @@ BarsVisualizationWidget::BarsVisualizationWidget()
m_fft_window = LibDSP::Window<double>::hann<fft_size>();
MUST(set_render_sample_count(fft_size));
// As we use full-overlapping windows, the passed-in data is only half the size of one FFT operation.
MUST(set_render_sample_count(fft_size / 2));
}
void BarsVisualizationWidget::context_menu_event(GUI::ContextMenuEvent& event)