Browsed by
Category: Research and Development

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…

Read More Read More

Infrasound processing with SoX

Infrasound processing with SoX

In this post I’ll cover how to use SoX to make low frequency sounds audible in a range that can be listened to. Infrasound is a low frequency sound wave that ranges from 20 hertz down to .1 hertz. Monitoring audio frequencies in this range is typically done to detect seismic activity that is caused either by nature or artificially, https://www.isla.hawaii.edu/sounds/ocean-sounds/. I have a sample of video that was shot with a Mobius camera. The audio range of the camera’s…

Read More Read More

Noise Filtering with SoX

Noise Filtering with SoX

In this post I’ll cover how to remove noise in an audio file using SoX. I’ll be using a Raspberry Pi which does not have an audio input by default. To get audio, I used an simple USB audio microphone to capture audio. The OS I’m running on my Pi is Ubuntu Mate and there was no need for anything to get the microphone to run. Once it was plugged in, I ran this command to view the properties of…

Read More Read More

Generating DTMF with SoX

Generating DTMF with SoX

In this post I’ll show how SoX can generate DTMF, (Dual-tone multi-frequency signaling) which is commonly used in phone and security systems. These dual tone signals are the foundation from which digital communications are based. The technology around DTMF is not complex. Lets cover the history of DTMF. DTMF was developed by Bell Labs and put in production in the early 1960’s. It was mostly used to replace pulse dialing systems that had limits on how far a phone could…

Read More Read More

SoX Noise Generation

SoX Noise Generation

In my last post I suggested creating noise and using a band of it to fill in a band gap. SoX provides a way to generate noise. There are different types of noise that SoX will generate. Lets take a moment to look at these types and what applications noise generation is used for. There are 3 main types of noise that SoX will generate, they are white, pink, and brown. White noise is a random signal that has equal…

Read More Read More

Sox Band-Pass and Band-Reject Filtering

Sox Band-Pass and Band-Reject Filtering

SoX provides many filters to process audio data. In this post I’ll be covering how to apply pass or reject filtering of frequency bands, commonly referred to as band-pass or band-reject. This filter will take a frequency or a range of frequencies and either remove them from an audio file or remove all other frequencies while keeping only them. I’ll cover 5 filters available in SoX that do this type of audio processing. Here is some information about each of…

Read More Read More

SoX – An Introduction

SoX – An Introduction

SoX, short for Sound eXchange, is a command line utility that can convert audio data into other formats. It can also apply various effects, play, record, mix, and filter the audio data. Refer to the development website, http://sox.sourceforge.net/. In a previous post I used it to create a spectrogram of an audio file using this command. sox audio-in.wav -n spectrogram Lets start with basic play operation. SoX can play audio data through the command line using the play command, here…

Read More Read More

Spectrograms with FFMpeg

Spectrograms with FFMpeg

In this post I’ll be covering how to create image files that represent the sound levels and frequencies of a media file. These images are known as spectrograms. They provide a way to visually locate moments in time. This can be useful for a number of reasons. FFMpeg has a feature that lets us create spectrograms with the showspectrumpic filter. Details about this filter can be found here, https://ffmpeg.org/ffmpeg-filters.html#showspectrumpic. You can also get information about the filter by typing in…

Read More Read More

Depthmapping with FFMpeg and OpenCV

Depthmapping with FFMpeg and OpenCV

Depthmaps are typically greyscale images that represent how far an object is by the degree of shade. They can be white-near, black-near, or some other color scale such as ironbar. Depthmaps are useful for creating renders or systems that have a distance sensing need. In this post I’ll be using footage that I shot using 2 Innovv cameras. The rig was not precise, so I also post processed it to correct distortion and alignment issues. The post processing topic was…

Read More Read More

Creating Anaglyph Video with FFMpeg

Creating Anaglyph Video with FFMpeg

In this post, we’ll step through how to create anaglyphic stereoscopic videos using FFMpeg. To create anaglyph imaging, we’ll need to use two camera sources, one left, the other right. These sources will be merged into a single image with red cyan overlaying to create a three dimensional effect using red cyan glasses. I referenced these sites frequently. FFMpeg Documentation – https://ffmpeg.org/documentation.html FFMpeg Stereoscopic Details – https://trac.ffmpeg.org/wiki/Stereoscopic The source video I’ll be demonstrating was shot with two Innovv C1 dashboard…

Read More Read More