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/Processor.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Noncopyable.h>
+#include <AK/StdLibExtras.h>
+#include <AK/Types.h>
+#include <LibCore/Object.h>
+#include <LibDSP/Music.h>
+#include <LibDSP/ProcessorParameter.h>
+#include <LibDSP/Transport.h>
+
+namespace LibDSP {
+
+// A processor processes notes or audio into notes or audio. Processors are e.g. samplers, synthesizers, effects, arpeggiators etc.
+class Processor : public Core::Object {
+    C_OBJECT_ABSTRACT(Processor);
+
+public:
+    virtual ~Processor()
+    {
+    }
+    Signal process(Signal const& input_signal)
+    {
+        VERIFY(input_signal.type() == m_input_type);
+        auto processed = process_impl(input_signal);
+        VERIFY(processed.type() == m_output_type);
+        return processed;
+    }
+    SignalType input_type() const { return m_input_type; }
+    SignalType output_type() const { return m_output_type; }
+    Vector<ProcessorParameter&>& parameters() { return m_parameters; }
+
+private:
+    SignalType const m_input_type;
+    SignalType const m_output_type;
+
+protected:
+    Processor(NonnullRefPtr<Transport> transport, SignalType input_type, SignalType output_type)
+        : m_input_type(input_type)
+        , m_output_type(output_type)
+        , m_transport(move(transport))
+    {
+    }
+    virtual Signal process_impl(Signal const& input_signal) = 0;
+
+    NonnullRefPtr<Transport> m_transport;
+    Vector<ProcessorParameter&> m_parameters;
+};
+
+// A common type of processor that changes audio data, i.e. applies an effect to it.
+class EffectProcessor : public Processor {
+protected:
+    EffectProcessor(NonnullRefPtr<Transport> transport)
+        : Processor(transport, SignalType::Sample, SignalType::Sample)
+    {
+    }
+};
+
+// A common type of processor that synthesizes audio from note data.
+class SynthesizerProcessor : public Processor {
+protected:
+    SynthesizerProcessor(NonnullRefPtr<Transport> transport)
+        : Processor(transport, SignalType::Note, SignalType::Sample)
+    {
+    }
+};
+
+}