Real-Time Audio Spectrum Analyzer

Visualizes microphone input in the frequency domain in real time, rendered as a bar chart in the terminal.

  Real-Time Audio Spectrum Analyzer   window: Hann   range: -80 to +0 dBFS
   0┤████                                                          ██        
  -4┤████ █                                                        ███       
  -8┤█████                                                        ████       
 -12┤██████                                                      ██████      
 -16┤███████                                                    ████████     
 -20┤████████                                                 ██████████     
     |        |        |       |      |     |    |    |    |   |    |
     20       50      100     200    500    1k   2k   5k  10k  20k

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Project Structure

RealTimeAudioSpectrumAnalyzer/
├── CMakeLists.txt                   # Root — FetchContent: KissFFT, PortAudio
├── build.bat                        # Build + run script
├── cmake/
│   └── spectrum_analyzer/
│       └── CMakeLists.txt           # Executable target, link rules
├── src/
│   ├── main.cpp                     # Entry point, render loop, CLI args
│   ├── audio/
│   │   └── AudioCapture.cpp         # PortAudio ring-buffer capture
│   ├── dsp/
│   │   ├── WindowFunction.cpp       # Hann / Hamming / Rectangular
│   │   └── FFTProcessor.cpp         # KissFFT wrapper → dBFS magnitude
│   └── display/
│       └── SpectrumDisplay.cpp      # ANSI terminal bar chart
└── include/
    ├── audio/
    │   └── AudioCapture.h
    ├── dsp/
    │   ├── WindowFunction.h
    │   └── FFTProcessor.h
    └── display/
        └── SpectrumDisplay.h

---

Dependencies

Library	Method	Purpose
PortAudio	FetchContent	Microphone input capture
KissFFT	FetchContent	Real-valued FFT (kiss_fftr)

No external installation required — cmake downloads the sources automatically on the first build.

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Build

Requirements

• CMake ≥ 3.22
• MSVC 2019/2022 (x64) or MinGW
• Internet access (for FetchContent on first build)

Building

build.bat              # Release
build.bat Debug        # Debug
build.bat Release clean  # Clean and rebuild

Running

build.bat run                              # default settings
build.bat run -- --window hamming          # Hamming window
build.bat run -- --fft 2048 --rows 30      # 2048-point FFT, 30 rows height
build.bat run -- --min-db -60 --max-db 0   # narrow the dB range

All Options

Option	Default	Description
--window	hann	hann / hamming / rect
--fft <N>	4096	FFT size (even number, power of 2 recommended)
--rate <Hz>	44100	Sample rate
--cols <N>	80	Number of frequency columns
--rows <N>	20	Display height (terminal rows)
--min-db <dB>	-80	Lower bound of the dB axis
--max-db <dB>	0	Upper bound of the dB axis

---

DSP Pipeline

Microphone
   │  (float32 PCM, 44.1 kHz)
   ▼
AudioCapture  ──ring-buffer──▶  readLatestFrame(N)
                                       │
                                       ▼
                              WindowFunction::apply()
                              (Hann / Hamming / Rect)
                                       │
                                       ▼
                              FFTProcessor::process()
                              kiss_fftr → |X[k]| → dBFS
                                       │
                                       ▼
                              SpectrumDisplay::render()
                              log-scale bar chart @ 30 fps

Parameters

Parameter	Value	Effect
FFT size N	4096 @ 44.1 kHz	Frequency resolution ≈ 10.8 Hz/bin
Window length	Same as N	Larger N → finer frequency, slower time response
Hann window	w[n] = 0.5(1−cos(2πn/(N−1)))	Sidelobe ≈ −31 dB
Hamming	w[n] = 0.54−0.46·cos(2πn/(N−1))	Sidelobe ≈ −41 dB
dBFS	20·log₁₀(	X[k]