Audio / Spectrum Analyzer

This RTA app supports simultaneous display of "Audio Waveform", as well as the FFT-based "Amplitude Spectrum" (frequency magnitude) and "Spectrogram" (frequency distribution over time), for audio signals input from a microphone.
(FFT: Fast Fourier Transform, RTA: Real Time Analyzer)

[Features]
- Supports simultaneous display of Waveform / Spectrum / Spectrogram.
- Supports orientation both portrait and landscape.
- Selectable configuration of Waveform / Spectrum / Spectrogram display.
- Selectable FFT size.
- Selectable Window function.
- Selectable Spectrum average.
- Selectable Frequency weighting. (Flat, dBA, dBC)
- Selectable the type of expressing the X direction (frequency) of Spectrum / Spectrogram. (Linear, Log)
- Displays the peak level and its frequency of the spectrum.
- Peak Hold (displays the results of holding past peak values ​​of the spectrum).
- Octave Analysis (displays the spectrum divided into octave bands).
- Generates the audio signal (Sine, Triangle, Squire, Saw)
- Generates the noise signal (white noise, pink noise)
- Pitch meter display.

The Pro version offers Ad-Free Viewing and High-Resolution Analysis (FFT size: 16384, 32768, Spectrum Average: 4, 8).

[Setting items]
1. Screen structure :
Select the display screen configuration.
View Num : 1, 2
View Type :
- 1 screen : Wave (Waveform) / 1D (Spectrum) / 2D (Spectrogram)
- 2 screens : W+1D (Waveform + Spectrum) / W+2D (Waveform + Spectrogram) / 1D+2D (Spectrum + Spectrogram)
Layout : Vertical (displayed vertically), Horizon (displayed horizontally)

2. Frequency Axis Scale Type :
Selectable the type of expressing the X direction (frequency) of Spectrum / Spectrogram.
- Linear: Distributed at equal intervals
- Log: The intervals increase logarithmically

3. FFT size :
1024, 2048, 4096, 8192, 16384, 32768
(* 16384, 32768 is available in the Pro version.)

4. Window function :
Selectable window function (multiplication just before FFT) used for spectrum calculation.
Hanning, Hamming, Blackman, No window

5. Spectrum Average
Number of spectrum average for a display of spectrum.
1, 2, 4, 8 (init value: 1)
(* 4 and 8 are available in the Pro version.)
Higher value will make the spectrum less noisy and more smooth, at the cost of lower time resolution.

6. Frequency Weighting :
Selectable frequency weighting.
- Flat: No frequency weighting is applied.
- dB(A): Frequency response that takes into account human hearing.
- dB(C): Relatively flat response.

7. Peak Hold :
Displays the results of holding the past maximum values ​​(peak values) of the spectrum.

8. Octave Analysis :
Displays the results of classifying the spectrum into octave bands.
Division method:
- FFT: Spectral display
- 1/12, 1/6, 1/3, 1 octave: Display divided into octave bands
Calc method:
- Max: Displays the maximum spectrum value in each band
- Average: Displays the average spectrum value in each band

9. Generates the audio signal :
Set the audio signal to be generated.
- There are 4 types of waveform. (Sine, Triangle, Squire, Saw)
- It can set the value of the frequency in 20Hz - 20000Hz.

10. Generates the noise signal :
Set the noise signal to be generated.
- There are 2 types of noise. (White noise, pink noise)

[Other]
- Background color: Black, White
- WaveForm: Line Color (Green, Yellow, Invert), Line Width (1.0 ~ 6.0 px)
- Spectrum: Bar color (Green, Yellow, Color patterns)
- Spectrogram: Colormap, Display range (-150 ~ -60 dB), Display time (4 ~ 60 sec)
- Bluetooth connection policy selection (disabled, HFP, A2DP).
- Scaling of Waveform / Spectrum display in the Y direction (magnification: 0.5 - 2.0).
- Scaling of Spectrum / Spectrogram display in the X direction (magnification: 1.0 - 16.0).

[Information]
- The vertical line spacing in the waveform display is 2 mSec.
- The calculation of spectrum and spectrogram uses the vDSP library.