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…
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…
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…