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Category: Raspberry Pi

RetroPie, Emulation Station, and Webmin

RetroPie, Emulation Station, and Webmin

Peter Carcione made a youtube clip last year about Game Wizard’s adaptation of RetroPie, a game console emulator that plays video games from the early days of gaming. It runs on a Raspberry Pi and provides an all inclusive interface to run the various console platforms. He provides a step by step that still works as of this writing, you can find it here One of the things that I noticed was that the distro that RetroPie ran on was…

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SoX Background Audio Monitoring – Triggered Recordings

SoX Background Audio Monitoring – Triggered Recordings

SoX offers quite a few ways to record audio. In this post, I’ll be covering how to record audio for the purposes of security. Home invasions are a sad fact of modern life for any number of reasons. I’ll show how to use SoX to capture audio so it can be added to the tools available to secure your personal belongings. One of the most simplest ways to get a recording from a microphone is to use the following commands….

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RF Spectrum Sweep

RF Spectrum Sweep

Identifying RF Channels to monitor can be a time consuming effort. Using a standard non PC radio receiver can take a long time to identify a transmitting channel. Using RTL_Power and SDR FFT Spectrum Logging provided here (http://kmkeen.com/rtl-power/), makes the effort less challenging. RTL_Power will sweep through a range of radio frequencies at given steps and log the RF power levels detected by the USB SDR receiver. It does this over and over at set intervals to create a log…

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RTL-SDR Radio Scanner

RTL-SDR Radio Scanner

In this post I’ll be giving some background and install steps on RTL-SDR. SDR stands for software defined radio and has been in use since the 1970s. Traditional radio processing is handled by hardware components like oscillators, regulators, and mixers. SDR replaces these functions with digital computer processing. RTL-SDR is a device that was originally designed to receive digital television transmissions, namely DVB-T TV using the RTL2832U chipset. The device is typically contained in a USB dongle. The RTL2832U chipset…

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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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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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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…

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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…

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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…

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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…

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