IMP Homework Podcast Episode One Transcript


My name is Wes Perdue, and I live in the East Bay area of San Francisco, California.

I enjoy learning about electronic music and audio production; this has become my hobby over the past few years. I'm taking a course online from Coursera titled Introduction to Music Production to enhance this knowledge. This six-episode podcast series will fulfill my weekly homework assignment for this class. The assignment is to re-teach a lecture from a list of available topics.

For the first week, I've chosen the topic Typical Recording Signal Flow in my Equipment, as I use my audio workstation weekly for a rather interesting application.

I record and publish a weekly podcast with my friend Hobbes. The podcast is called Late Night Geekery. We record the podcast on Monday nights from our homes over Skype. In addition to recording, we live stream the podcast to our dedicated audience. We've been doing this for about a year now, and the production is continually evolving, as I learn new things.

I will now describe the signal flow for this podcast. If you'd like to follow along, I've created a signal diagram in PDF form, which is linked in the show notes. You can find the show notes on my blog at

Hobbes is in his home studio sitting in front of his ADK A-51 microphone; it is connected to his Motu 828 audio interface via XLR cable, which is connected to his Macintosh via Firewire.

I am in my home studio in front of my ADK Vienna mic, which is connected to my Motu 4pre audio interface, which is connected to my Macintosh via Firewire.

Outside the box

My voice travels through the air into my microphone, where it is converted into an analog audio signal. My mic is a condenser, so it needs phantom power, which my Motu provides. The audio signal goes through an XLR cable into the preamp in my audio interface, where the signal is boosted to line level. The signal then goes into an analog to digital converter, and the interface sends that digital audio signal over the Firewire interface into the computer for processing.

In the box

My Motu is set as my Mac's system audio input and output, so signal routing within the computer is relatively simple, with two exceptions: I'm recording the podcast over Skype, and I'm sending out a live stream.

First I'll discuss the Skype recording.

I hijack Skype's audio input and output with Audio Hijack Pro. This allows me to record Skype's input and output as separate channels in a single file. Later, I'll import that file into Logic, add the intro theme song, mix the two channels, and output it to a compressed file so it can be downloaded via a podcast app like iTunes, Instacast, or Downcast.

Audio Hijack sends my signal to Skype, which sends my signal across the Internet to Hobbes's computer. There, his Skype app sends his signal to me.

My Skype app receives his signal and sends it via Firewire to the headphones output on my Motu audio interface. A digital to analog converter in my Motu 4pre converts his digital audio signal to analog and puts it out the headphones port. My headphones receive the analog signal and convert it to audio that I hear. My headphones are a transducer. They are also sealed, or closed, so my microphone doesn't pick up the audio signal and feed it back into the mix.

In addition to writing both of our audio signals to a file for offline processing, Audio Hijack sends our signal via a Soundflower bus to Logic for live mixing. Logic then outputs our mixed signal onto another Soundflower bus to Nicecast. Nicecast encodes and compresses our mixed signal for live streaming and sends that signal to a Shoutcast server I host on a virtual machine at my ISP.

Our live listeners can click on a link to receive that live stream signal in their web browser. Their web browser sends that signal to their host operating system, which sends the mixed stream to their sound card. The sound card converts the signal to an analog audio signal, which is then sent to headphones or speakers.

In addition, our listeners can interact with us live in our podcast's text-based chat room. This completes the circle of communication and adds greatly to the show with live feedback.


In the simplest sense, audio goes in through our microphones, where it's converted from audio to an analog electrical signal, and then through our audio interface where it's converted to digital. It goes through our computers to Skype, where it's sent across to the other computer, where the process is reversed, and the audio signal is sent to our headhones. In addition, Audio Hijack Pro grabs both channels and writes them to a file for offline processing. It also sends both channels to Logic where they're mixed and then sent to Nicecast, which sends the mixed signal to the streaming server, where people can connect with one click and listen live.

Thank you for listening. If you'd like to submit feedback for this podcast, please use the contact form at