Spectrum Analyzer for iOS

Spectrum Analyzer for iOS is a powerful real-time audio analysis app. Designed with musicians and recording engineers in mind, it can also be used by anyone interested in the world of sound. Ideal for room tuning or speaker tuning, the app enables portable, precision audio measurement and visualization. The videos below demonstrate three of the included modules - Octave RTA, FFT Plot, and Spectrograph. A Test Tone Generator is also available.
 


Octave Band RTA (Real-Time Analyzer)

Octave RTA Splits the audible range into frequency bands. It supports ISO Octave bands from Full to 1/6 Octave. Two graphics modes are supported: Classic mode, where bands are drawn as simple bars; and Modern mode, where the whole spectrum is represented by a colorful analog graph (continuous visible light spectrum from red to violet). Other configuration options include: FFT Size, Time Averaging/Decay Mode, and Peak Tracking.


FFT Plot (Fast Fourier Transform)

FFT module plots real-time raw spectrum graph. It is useful for detailed analysis and isolating particular frequencies. Options include FFT Size, Averaging Mode, Logarithmic or Linear Frequency Scale, and FFT Window function (Hamming, Blackman, or Rectangular). Again, Cursors, Peak Tracking, and dB offset are supported, as well as input channel selection.


Spectrograph

Spectrograph module plots frequency over time spectrograms of surrounding sounds, music, etc. It can be used to reveal images "hidden" in sound. Options include Decade or Linear Scale, Speed, and Gain adjustment. Several Color Palettes are available suiting different applications.




FFT Size and Averaging

Choosing the right FFT Size and Time Averaging is always a trade-off between time and frequency resolution. The more accurate the frequency resolution (larger FFT size), the less accurate the time resolution and vice versa.

For rapidly changing material such as music and speech, FFT size of 2048 or 4096 and averaging set to Fast or Medium will do fine.

For test signals, such as pink noise and constant frequency tones, a larger FFT (8192 or 16384) with Slow or Infinite averaging works best. Larger FFT Size also provides better low-end frequency representation.


Audio Input and Settings

Audio input may be acquired via the built-in microphone or an external measurement microphone. For best results we recommend using a calibrated measurement microphone connected via USB audio interface or iPhone dock connector. This allows for high precision and flat frequency response, as well as for stereo input.

The active audio device is shown in the middle of the top status bar. Tap to open the Audio Settings dialog.




Recommended Microphones

For a quick reference get an inexpensive external mic such as Dayton Audio iMM-6 which is compatible with the iPhone and plugs directly into the headset jack.

Pro users may consider using a dedicated measurement mic such as miniDSP UMIK-1 Measurement Microphone. Each unit comes with individual calibration file, a tripod and USB cable. Requires Lightning to USB Camera Adapter.




Microphone Calibration

Octave RTA and FFT modules support real-time microphone frequency response compensation:

For information on file format used and sample .cal files, please visit this page.