feat(audio): Implement real-time spectrogram synthesizer

Adds a multi-voice, real-time audio synthesis engine that generates sound from spectrogram data using an Inverse Discrete Cosine Transform (IDCT).

Key features:
- A thread-safe, double-buffered system for dynamically updating spectrograms in real-time without interrupting audio playback.
- Core DSP components: FDCT, IDCT, and Hamming window functions.
- A simple sequencer in the main loop to demonstrate scripted audio events and dynamic updates.
- Unit tests for the new synth engine and Hamming window, integrated with CTest.
- A  file documenting the build process, features, and how to run tests.

1 files changed, 29 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b5ac51e..c9b8cad 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,10 @@ add_executable(demo64k
     src/platform.cpp
     src/gpu/gpu.cpp
     src/audio/audio.cpp
+    src/audio/fdct.cpp
+    src/audio/idct.cpp
+    src/audio/window.cpp
+    src/audio/synth.cpp
 )
 
 target_include_directories(demo64k PRIVATE
@@ -30,3 +34,28 @@ if (DEMO_SIZE_OPT)
         target_link_options(demo64k PRIVATE -Wl,--gc-sections -s)
     endif()
 endif()
+
+option(DEMO_BUILD_TESTS "Build tests" OFF)
+enable_testing()
+
+if(DEMO_BUILD_TESTS)
+    add_executable(test_window
+        src/tests/test_window.cpp
+        src/audio/window.cpp
+    )
+    target_include_directories(test_window PRIVATE
+        src
+    )
+    add_test(NAME HammingWindowTest COMMAND test_window)
+
+    add_executable(test_synth
+        src/tests/test_synth.cpp
+        src/audio/synth.cpp
+        src/audio/idct.cpp
+        src/audio/window.cpp
+    )
+    target_include_directories(test_synth PRIVATE
+        src
+    )
+    add_test(NAME SynthEngineTest COMMAND test_synth)
+endif()