Today I finally figured out how to use an Audio Unit plug-in in the signal path of my speaker testing software. I thought I'd share this for others who might want to do the same thing.
My project is to develop stereo speakers where the crossover and equalization are done in software before the amplification stage. The miniDSP platform might be an good solution for some, but I am using professional drivers with somewhat ragged raw response, and I want to be able to incorporate room EQ adjustments as well. The Audio Unit plug-in FabFilter Pro-Q provides great flexibility in the number and types of EQ curves available, and also permits individual adjustment for each channel. And the user interface for this plug-in is superb.
The problem I had was to find a way to route the audio test signal through the plug-in equalizer so that I could observe the effects of my adjustments as I made them.
The hardware I'm using is an early Intel Mac mini (ca. 2007, I think) with the current version of Snow Leopard installed and a MOTU 828 Mk II FireWire audio interface, which was a state-of-the-art recording product when I bought it ten years ago. I am using a Behringer EM8000 microphone through the MOTU 828 to capture test tones.
The software combination that eventually worked for me is Soundflower (a freeware audio routing utility for the Mac), Logic Express 9, Fuzzmeasure Pro (free demo, $150 to buy), the Fidelia music player (free demo, $20 to buy), and the FabFilter Pro-Q plugin (free demo, $199 to buy). The last three are all running in free demo mode.
Here are the steps I took that ultimately allowed me to use the plug-in iteratively in the audio path for my tests:
1) I downloaded and installed Soundflower, the freeware audio routing utility from Cycling 74.
2) In Audio Midi setup, I selected Soundflower (2 ch) as the input source and the MOTU 828 as the output source. For a long time, every time I selected the bidirectional MOTU 828 for either input or output in Audio Midi setup, it would automatically default to both input and output. Then I discovered that the little gear icon at the bottom of the Audio Devices window would allow me to split the input and output between different audio devices.
3) I opened a new project in Logic Express and created a single audio track. In the Audio Preferences pane, I selected Soundflower (2 ch) as the input, and the MOTU 828 as the output. I turned on monitoring for this track so that any audio that appeared at the input would be routed to the output. I also opened an instance of the FabFilter Pro-Q plug-in on this track. Therefore any audio that flowed through this track (including the swept-sine signal from the test software) would be affected by the plug-in settings.
4) I opened Fuzzmeasure Pro and clicked the "Capture Settings" icon along the top edge of the main window. In the window that opened, I selected Soundflower (2 ch) as the Playback Device and set it to channel one. I selected the MOTU 828 as the Record Device and set it to channel two.
5) I plugged my measurement microphone into channel two of the MOTU 828, dialed back the output gain, and clicked the "Measure" icon in Fuzzmeasure Pro. Much to my delight, I heard the sine-wave sweep from my speaker and, a few seconds later, saw the frequency and impulse response graphs appear in Fuzzmeasure Pro.
6) I opened the FabFilter plug-in in Logic Express and started making my adjustments. After twenty iterations or so, I had a setting that I wanted to try with real music (and I was getting pretty sick of the sine sweeps by then, anyway). I saved the settings of the FabFilter plug-in to my desktop.
7) I then opened my demo copy of Fidelia. One neat thing about Fidelia (and there are quite a few) is that it can host up to three different plug-ins, which it calls "effects." I opened the first effect and navigated through the menus to my Audio Unit FabFilter plug-in. I clicked on Presets at the top of the FabFilter window, then navigated to the saved version of the plug-in settings on my desktop. They opened perfectly, and voila, I was listening to music through the same EQ settings that I had developed through my sine sweep experiments in Logic Express.
Apologies to anybody who finds this to be too elementary, but I searched far and wide (and long) without finding any practical advice on how to do what I managed to do today. I would think that a growing number of DIY fans might be interested in pure software solutions for tailoring both near-field and in-room response.
