The NSA Selector

Summary

the NSA selector you can purchase the NSA selector at my little shop over at lectronz. what is it the NSA selector is a eurorack module with two ethernet jacks and one audio output. any bit on the network will be sent to the audio output. what it's not this is not an "audio interface". we do not play back any "format" such as RTP or MP3 or WAV ot the like. the eurorack module does not "speak" any protocol. all traffic is forwarded from one network jack to the other unmodified. it's just tapped, intercepted to convert it to audio. examples watch the NSA selector video sequencer script in the folder sequencer/ you find a very simple shell script, that mimics a sequencer by network pings of different size. plain image transfer if we transfer uncompressed, unencrypted images e.g. in the .bmp format, we can hear the pixels. together with a small http server which is available in the fileserver/ folder. you can listen to your photos or drawing from gimp (or photoshop in case you're a rich musician). encode audio to NSA's native format the NSA selector's native format is 4 bits and 25MS/s which originates from the typical PHY MAC interface called MII. at first glance 4 bit audio appears to be really crappy, but we can use the ridiculously high sample rate. what we need is called a delta-sigma modulator. this lets us convert a simple mono 16 bit 48kHz .wav file to a 4 bit 25MHz .nsa file. note that this saturates the link and through the added headers from ethernet, IP, UDP or TCP and HTTP you'll get artifacts. and happy litte retransmissions. far from HiFi quality, but the method adds a lot of spice and excitement. there's a converter in the upconverter/ folder. network overhead here's what a network packet can look like on the wire: and we're listening in on the "4B" side of the "4B5B encoding" layer. so the first bits we hear are the preamble of the ethernet frame and we follow up the stack. e.g. ethernet, IP, TCP, HTTP, BMP. delay, oversaturation there's a neat little i...