Following the recording tools theme of the last post (Esession Virtual Glass AU plug-in test), this post looks at another alternative approach to mixing multiple audio sources on the Mac and doing a remote, collaborative, 2-way recording/production session. Rather than the integrated approach of Virtual Glass and other DAW collaborative plug-ins, this time I am looking at how to "roll your own" DIY audio monitoring solution using Skype and Ambrosia's WireTap Anywhere combo. The beauty of this approach is that in addition to your DAW, you can also add any number of other audio application sources/inputs you may want to use such as BIAS Peak or iTunes or even in-browser streaming audio or headset(s). With WireTap Anywhere, since it is implemented at the system level as a kind of easy, on-the-fly audio aggregate device editor, you can also add or remove audio sources in realtime without disconnecting the Skype call.
THE CHALLENGE
Essentially the challenge looking for a solution was simply this: How do you mix multiple audio input sources from mic & Mac OS X applications to Skype's single input source menu? Skype presents it's own single input source from within the application, so how can we enable a producer/engineer/musician to both talk and easily playback multiple audio sources/mixes/tracks at the same time so that a remote listener/collaborator can instantly monitor/discuss the work in progress.
It turns out that there are actually a couple of different viable solutions of varying complexity and both involve creating a virtual input mixer and therefore a "custom" audio source for Skype. There could in fact be more alternatives, but after some thought and searching, these were the two I personally pursued and successfully got to work (thanks to Nate Tschetter for perseverance and joint brainstorming)!
This particular solution is the lowest cost but requires 2 applications from Rogue Amoeba and Cycling 74. The detailed setup and approach is very well documented on the following Technosailor blog post so I will not repeat it here. The only screenshot/info missing is the need to enable Hijack and Monitoring from within the Application Mixer when you open it, so that you can hear what you are mixing. With this approach, you can independently mix multiple sources and use soundflower as the internal digital mixer to sum them. (You then select the Soundflower 2CH input to Skype under Preferences, Audio Tab.)
SOLUTION 2: WireTap Anywhere ($129) & Skype (FREE)
This second method is far simpler, more elegant, and much easier to setup though it is an admittedly more expensive solution. This hinges on Ambrosia Software's WireTap Anywhere - a visual audio input aggregator. However, this does have a FREE 30-day demo to try it out.
Once the software is installed, you will find it not in the Applications folder but under the Apple menu, System Preferences in the "Other" pane at the bottom of the System Preferences window. Click on the icon and the WireTap single-screen setup interface will open.
Click the "+" button to add an audio source, name it and then add as many SW applications or HW devices as you like and these will all "aggregate".
Finally, go to Skype, Preferences, Audio Tab and select the new composite Audio Source you have created and named from the Audio Input menu list. Easy huh?!
OS X & AGGREGATE AUDIO DEVICES
One of the big bonuses of this alternative approach is that it turns out that you can apparently add new input devices (such as a bluetooth or USB headset) on-the-fly while already on a call without disconnecting Skype. For example, this would allow you to add sources or more people. This therefore allows 2 or more applications or users to communicate over a single connection using mutiple headsets (eg. Producer & Artist or members of a band giving everyone basic talkback and monitoring!).
Potentially, I guess a whole band or multiple collaborators at either end of the Skype call could be outfitted with wireless headsets like the FreeTalk - I may have to try this in future and report back on what the practical technical challenges/implications are!
AUDIO COMPRESSION/CODECS & FREQUENCY RANGE/BANDWIDTH
NOTE: ** These initial tests were performed using Mac OS X BETA 2.8.0.324 which uses a variety of legacy audio codecs including G.729 & SVOPC. However, Skype v4.0 on PC and the latest Mac OS X BETA BUILD 2.8.0.438 includes the new "super-wide bandwidth" SILK codec.
Before you get too excited, while SILK is definitely able to handle music sources with audible additional clarity and bandwidth, it is a 24kHz Sample Rate giving 12kHz audio bandwidth. However, in practice this is fine for listening to a radio-friendly mix test (FM Radio is only 15kHz bandwidth).
Skype can also occasionally speed-up/slow-down momentarily while rebuffering (would be great to turn this off for music applications) and the encode/decode sample rate's are variable based on network conditions (again would be great to lock this), however these are the pitfalls of using consumer VOIP for audio mix/recording applications. I was going to coin the term MOIP for Music over Internet Protocol, but lets just say a certain urban lexicon steered me rapidly away from that particular acronym. ROIP has already been deemed for radio so perhaps for now we will leave this recording solution nameless!
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