Libraries: Add LibDSP

LibDSP is a library for digital signal processing, and is primarily
intended to support the future DAW version of Piano.

Userland/Libraries/LibDSP/Effects.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Processor.h"
+#include "ProcessorParameter.h"
+#include "Transport.h"
+#include <AK/Types.h>
+
+namespace LibDSP::Effects {
+
+// A simple digital delay effect using a delay buffer.
+// This is based on Piano's old built-in delay.
+class Delay : public EffectProcessor {
+public:
+    Delay(NonnullRefPtr<Transport>);
+
+private:
+    virtual Signal process_impl(Signal const&) override;
+    void handle_delay_time_change();
+
+    ProcessorRangeParameter m_delay_decay;
+    ProcessorRangeParameter m_delay_time;
+    ProcessorRangeParameter m_dry_gain;
+
+    Vector<Sample> m_delay_buffer;
+    size_t m_delay_index { 0 };
+    size_t m_old_delay_size = m_delay_buffer.size();
+};
+
+// A simple effect that applies volume, mute and pan to its input signal.
+// Convenient for attenuating signals in the middle of long chains.
+class Mastering : public EffectProcessor {
+public:
+    Mastering(NonnullRefPtr<Transport>);
+
+private:
+    virtual Signal process_impl(Signal const&) override;
+};
+
+}