Measuring Audio Unit Effect Plug-ins With Electroacoustics Toolbox


Measuring Audio Unit Effects Plug-ins Using Electroacoustics Toolbox, Soundflower, and AU Lab

A valuable use of Electroacoustics Toolbox is measuring Audio Unit effects. Measuring Audio Units can be useful to developers of such plug-ins, or to anyone employing Audio Unit effects in their digital audio recording, editing, or reproduction system.

This tutorial requires two free software packages in addition to the Toolbox: Soundflower and AU Lab. AU Lab is distributed with Tiger (Mac OS X, 10.4).

Soundflower is a free system extension for Mac OS X, version 10.2 or later, that allows for convenient routing of audio signals between applications on the Mac. More information regarding Soundflower, as well as a download link may be found at (Version 1.2 was employed at the time this tutorial was written.)

AU Lab is a digital mixing application, designed as a reference Audio Unit host for those wishing to develop their own Audio Unit plug-ins or Audio Unit hosting applications. AU Lab is provided free of charge with the Apple Developer Tools. After installing the Apple Developer Tools, AU Lab can be found in the directory /Developer/Applications/Audio (that’s the Developer directory at the root level of the hard drive). Documentation for AU Lab should be available from the same directory. (Version 1.0.3 was employed at the time this tutorial was written.)
The rest of this tutorial assumes that Soundflower and AU Lab are installed and ready for use. Please refer to the Soundflower, AU Lab, or Electroacoustics Toolbox documentation for further assistance with each program.

Configuring AU Lab
1. Launch AU Lab.
2. If the Create New Document window appears, continue to step 3. If not, select New from the File menu, or type Command-N.
3. In the Audio Device popup menu, select Soundflower (16ch).
4. In the Outputs tab, change the Output Channels popup menu selection to Mono.
5. Click the Add Output button.
6. Place the two mono output channels under channels 1 and 2.
7. Make sure the output settings look like those in Figure 1.

Figure 1: AU Lab - Creating New Output Channels

8. Click on the Inputs tab to view the Audio Input Settings.
9. Click the Add Input button twice to create two new input channels.
10. Drag the two red squares so that both of the two input channels appear under channel 3.

Figure 2: AU Lab - Creating New Input Channels

11. Click OK to create the new AU Lab document.
12. In the AU Lab document window, click the small “1” and “2” buttons under Volume in the Audio 2 input track. This will remove Audio 2 from Master Output 1 and add it to Master Output 2.
13. Go ahead and save the new AU Lab document by selecting Save from the File menu, or typing Command-S. Save it with the name SFOut12In34.trak for easy reference in other Electroacoustics Toolbox tutorials.

Figure 3: AU Lab - Document Window

Configuring Electroacoustics Toolbox
1. Launch Electroacoustics Toolbox.
2. Create a new project if one was not created automatically when the program launched.
3. Click the Device IO button in the project window toolbar to open up the Device IO Setup window.
4. In the Device Setup window, click on Soundflower (16ch) in the Available Devices list. This will display the Soundflower (16ch) properties in the lower portion of the window.
5. Make sure the Soundlfower (16c h) nominal sample rate is set to 48 kHz.
6. Create a new Dual FFT Analyzer tool. This can be accomplished by clicking the “Add” button () in the Dual FFT Analyzer row of the project toolbox, selecting Dual FFT Analyzer from the Tools menu in the project window’s toolbar, or by selecting New Dual FFT Analyzer from the Tools menu (or by typing Command-1).
7. Select Soundflower (16ch) from the Input Device popup menu in the signal drawer of the Dual FFT Analyzer.
8. Select Soundflower (16ch) channels 1 and 2 in the Live Data Sources box (they will probably already be selected). Recall that Soundflower (16ch) channels 1 and 2 were chosen as output channels in the AU Lab document. This will allow AU Lab to route signals directly to the Dual FFT Analyzer’s input channels via Soundflower.
9. In the Excitation tab of the Dual FFT Analyzer’s controls drawer, select output channel 3 of the Soundflower device in the Output Channel popup menu.
10. Start the analyzer, either by clicking the start icon in the window’s toolbar, or by selecting Toggle Tool On/Off from the Control menu (or by typing Command-R).
11. At this point, a flat line should be visible in the Dual FFT Analyzer’s display, since the default measurement is Transfer Function Magnitude and AU Lab is just sending the two (identical) signals back to Electroacoustics Toolbox without altering them in any way.
12. Go ahead and save the Electroacoustics Toolbox project by selecting Save Project from the File menu, or typing Command-S. Save it with the name SFOut12In34.featproj for easy reference in other Electroacoustics Toolbox tutorials.

Figure 4: Electroacoustics Toolbox – Signal Generator 's Swept Sine Configuration

Measuring an Audio Unit Effect
Now that AU Lab and Electroacoustics Toolbox are both configured for the measurement, measuring any available Audio Unit effect is quite simple.
1. In AU Lab’s Audio 2 track (in the SFOut12In34 document created previously), select the desired Audio Unit effect from the first Effects popup menu. The document window should look like Figure 5.
2. As the effect’s parameters are adjusted, the changes will be immediately reflected in the Dual FFT Analyzer. As an example, Figure 6 includes a screenshot of the AUGraphicEQ effect being measured by Electroacoustics Toolbox.

Figure 5: AU Lab -- Final Document Window Configuration

Figure 6: Measuring the Frequency Response of the Graphic EQ

This article was originally published in the forums for an earlier version of Electroacoustics Toolbox. The content still applies to the latest version of the Toolbox.


  • Jignesh

    Hi, I am home theater installer and planning to buy RTA. I saw your software and found really very good for measuring the audio.

    My question is, do I need a hardware (apart from MacBook) to run this software?
    Yes, I need recommendation!

    I was planning to buy GoldLine TEF25. Is TEF25 OK with this software?

    Thanks in advance.


    • ben

      My question is, do I need a hardware (apart from MacBook) to run this software?
      I was planning to buy GoldLine TEF25. Is TEF25 OK with this software?

      To connect an external measurement microphone, you’ll need some type of external audio interface, but I don’t believe the TEF25 is Mac-compatible. You might want to take a look at the MOTU Ultralite or the RME Fireface 400/UC as a high-quality alternative.

  • arenno

    how about dewetron (Digital signal analyzer), is it compatible for these app?

  • Doug Hall

    Any plans to update this? I found it hard to follow because the GUIs in the latest versions of Electroacoustics Toolbox and AULab have changed. Or is this now superseded by options in the newer version (It seems the option to apply an AULab filter in the signal generator does nearly the same thing).