WithStrings Audio Analyzer

1. Description

Audio Analyzer acquires a signal from the device's microphone and displays its time-history and Fourier amplitude frequency spectrum (using a FFT algorithm). Sampling of the time history starts when the amplitude of the audio acquired at the microphone is greater than the adjustable trigger level slider. The length of acquisition is adjustable from 0.05 seconds to 1 second. Vertical scales for each of the graphs are independently adjustable or can be set to auto-scale. A cursor for each graph has three settings: off, find peak or find value using a slider. Linear or logarithmic amplitude displays are available for the vertical axis of the frequency graph. Data from the graphs are 4096 points and can be saved to a spreadsheet compatible formatted file.

2. Operation

Launch the application. Audio Analyzer will display a screen similar to figure 1. The cursors are initially off, frequency range is set to 20Khz, and vertical scales are set to auto mode. Pressing the Run button will start acquisition if the input amplitude is greater than the trigger level. Adjust the trigger level for the desired sensitivity by moving the red circle on the trigger slider.

The Freq(Time) button produces inverse results on the time and frequency graph. A wide frequency setting of 20Khz will produce a very small time sampling window of 0.05 seconds. Conversely a 1Khz frequency range will produce a sampling window of 1 second.

A cursor is available for each graph. The default setting is off. Pressing the cursor button one time will set it to peak mode. The peak (positive) will be shown on the graph with cross-hairs on the graph; its x,y coordinates are displayed in blue font on the upper right side of the graph. Pressing the cursor button again will allow the cursor cross-hairs to be dragged to any data point on the graph. The x,y coordinates of this point are displayed in blue font on the upper right side of the display.

Vertical scales are adjustable for each graph. Auto mode will find the best scale to display all of the datum on the graph. Pressing the scale button will set the vertical scale to one of several predefined scales.

The Lin/Log button when set to log mode shows the vertical scale equaling the log of the value. This is ideal to find small frequency peaks that are otherwise buried in the spectrum display.

The Save Data button will capture the time and frequency graph to a comma separated variable file in the following directory: /mnt/sdcard/Android/data/com.withstrings.audioanalyzer/files. Note all data in this directory will be erased if the app is un-installed.

3. Characteristics

Operating System: Android: Minimum API 9, Gingerbread
Permissions: WRITE_EXTERNAL_STORAGE, RECORD_AUDIO
Max Acquisition Rate: 44100 samples/s, Number of Samples: 4096 @ 20KHz(0.05s)
Min Acquisition Rate: 2756 samples/s, Number of Samples: 4096 @ 1KHz(1s)
Settings:
Run/Pause
Trigger Slider: 0 to 100% of sampled RMS value.
Time Graph Vertical Scales: 32K, 16K, 8K, 4K, 2K, 1K
Freq Graph Vertical Scales: 64M, 32M, 16M, 8M, 4M, 2M
Freq Graph Vertical Scales (Log): 8, 7, 6, 5, 4, 3
Freq/Time Scales: 20KHz(0.05s), 10KHz(0.1s), 5KHz(0.2s), 2KHz(0.5s), 1KHz(1s)
Cursor: Off, Peak, Slider
Save Data writes to the following file in Pause mode:
/mnt/sdcard/Android/data/com.withstrings.audioanalyzer/files. External devices must not be connected to the usb port when saving data.
Identity: sin(u)sin(v) = 1/2[sin(u-v) + sin(u+v)]
Graphics Design: N. Dynamite


© 2015 Todd Merport