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Requirements: Android 1.5 and up
Overview: SPL & RT60 Meter, Spectrum Analyzer & Signal Generator
Features 1/3 octave, spectrogram, peak freq., fast, medium & slow filters, flat & A/C Weighting, Averaging, SPL Chart Recorder, White/Pink Noise, sine/square/triangle/ramp/impulse signals. Frequency spectrum store & load, von Hann windowing, "Keep Screen On"
Use: home theater, audio engineer, car audio, etc
AudioTools's Spectrum Analyzer component uses FFT on batches of samples recorded at the microphone. Hann windowing reduces aliasing. Recorded spectra may be stored as files on the SD card, and then loaded later and displayed together with the live spectrum.
(The "Store" button will store the current live spectrum with a filename of your choice. The "Load" button brings up a list of stored spectra. One of these can be chosen, or the "Cancel" item selected to return to the main display, or the "Clear" item selected to remove the currently loaded spectrum.)
Data collection can be paused and restarted.
The deciBel meter component uses IIR filters and exponential averaging to calculate Flat, A and C weighted response at speeds of Fast, Medium and Slow.
The Chart Recorder shows a moving trace of the SPL measurements over the last couple of minutes.
RT60 measurements can be made by starting the RT60 component and using a loud clap (or similar) to trigger the measurement. RT60 times measure how much reverberation or echo there is in a room or auditorium.
The Signal Generator component of AudioTool generates White and Pink Noise, Sine, Square, Triangle and Ramp waves, and Impulses. The generator uses multiple cycled buffers that are refreshed randomly so ensuring truly random White/Pink noise. The Pink Noise algorithm uses Kemmet's method to adjust White Noise into Pink.
Wave frequency is set using the arrow buttons or directly via the keyboard. The upper display shows the sound picked up by the microphone in real time. This can be useful for evaluating the response to an audio system being fed with the generated sound. Better results can be obtained by using a headset adapter/splitter that allows an electrical signal to be sent from the device to the audio system.
The Impulse signal is a delta issued approximately once per second. Impulses can be used to measure the frequency response of audio systems: they have a flat frequency distribution.
The accuracy in frequency of the generated periodic signals is quite good: on the Motorola Droid, errors were of the order of 1% throughout most of the range. Sine wave fidelity is good throughout most of the audio range. Other signals' leading and trailing edges show ringing and decreasing frequency response artefacts in the upper ranges.
NOT recommended for Samsung Androids