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Month: November 2017

Decoding DTMF with MultiMon-NG

Decoding DTMF with MultiMon-NG

Dual Tone Multi Frequency signaling, commonly referred to as DTMF, is mainly used for phone dialing systems. But this isn’t the only use for DTMF signaling. Another common use is security access systems. In this post, I’ll be covering how to decode DTMF using MultiMon-NG. SoX will be used to record the DTMF signals generated on cell phones and keyless entry systems. I’ll be using a high gain directional microphone with a secondary microphone to cancel out background noise. SoX…

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Sonic data analysis with SoX

Sonic data analysis with SoX

In this post I’ll be using SoX to export audio to data values that can be processed outside the audio realm. The example I’ll use here is a breif recording that will be plotted with GNUPlot. SoX and other programs provide spectrograms, which are frequency domain images of audio files. I’ll be using GNUPlot to create an image of an audio file in the time domain. First, I’ll use this command to convert the audio wav file into a text…

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Noise Cancelled Microphone with SoX

Noise Cancelled Microphone with SoX

In this post I’ll be using two USB microphones to record audio, one for the intended sounds I wanted to record, the other to capture background noise that I want to filter out. I’m using two cheap USB embedded microphones that I bought for less than $10 each, http://a.co/eIsnp3Z. The machine I’m recording on is a Raspberry Pi 3 running Ubnutu Mate. Since the Raspberry Pi doesn’t have an audio in device built in, I selected the USB microphones. These…

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Ultrasonic SoX

Ultrasonic SoX

This post will be quick and to the point. We’ll be using SoX to bring high frequency audio, commonly referred to as ultrasound, down to a range that can be heard. First thing I did to validate the process was generate an ultrasonic data file using Audacity. The problem with the standard 44.1k sampling rate is ultrasound frequencies will be dropped. I created my data files with a sampling rate of 192k. play “/home/local/Desktop/Ultrasound/Audacity192k_33khz.wav” Playing audio from this sample is…

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