Free audio spectrum analyser for your microphone.
No ads. Full version.

64 up to 8192 frequency divisions (128 to 16384 FFT size).
22 kHz spectrum range (can reduce down to 1 kHz for higher resolution).
FFT Windowing (Bartlett, Blackman, Flat Top, Hanning, Hamming, Tukey, Welch, or none)
Auto-scale or pinch to zoom, drag to pan.
Linear or logarithmic scales.
Peak frequency detection (polynomial fit).
Averaging, Min and Max.
Save CSV data files (uses Write External Storage Permission).
Free or snap to peak cursor.
Octave Bands - Full, half, third, sixth, ninth or twelfth bands.
Weighting – A, C or None (A weighting filters the high and low frequencies according to how the ear perceives sound loudness).
Musical note indicator (green if within 5 cents, orange if within 10 cents).
Auto-scaling microphone input trace.
For best response on slower devices, keep the FFT size low.

More detailed explanation available on website