Getting Started with FuzzMeasure Pro

Software Requirements

Operating System

FuzzMeasure Pro requires Mac OS X 10.5 Leopard to run. Keeping up-to-date with the latest software updates is important, so be sure to install them as they come out. FuzzMeasure may add features or benefit from fixes that are only available in the latest software updates.

Computer

FuzzMeasure Pro should run fine on any system that can run Leopard (at least a G4 867MHz, 512MB or higher). FuzzMeasure is tested on a PowerBook G4 1.5GHz with 2GB RAM periodically for performance and compatibility, but if issues are found on other configurations, please file a bug.

Intel-based Macintosh computers can run FuzzMeasure Pro with great ease, as FuzzMeasure thrives on high memory bandwidth. FuzzMeasure also takes advantage of multiple cores when it can, so Mac Pro owners will enjoy very snappy performance in otherwise-intensive operations (such as calculating waterfalls).

Your choice of GPU does not factor into FuzzMeasure's performance. Even the 3D waterfall display works great on integrated graphics chips like the Intel GMA 950 that came with first-generation MacBook computers.

NEW! Videos!

We have published a set of videos that demonstrate the basics of getting FuzzMeasure set up for acoustic measurements. Watch the videos on YouTube now.

Audio Hardware

Overview

In order to use FuzzMeasure, you require an audio interface to get audio signals in and out of your Mac. For some systems, you can use the built-in audio hardware to perform electrical measurements, and add a microphone preamplifier for acoustic measurements.

This guide will focus on the use of an external audio device with FuzzMeasure Pro, as this represents the most common setup. The ART USB DualPre is featured in the demonstration images, but since other devices have very similar connection schemes, anyone can follow along with this guide.

Attaching Your Device

Every device is different, so you will have to rely on whatever documentation you received when you got your hardware. The DualPre device does not ship with documentation or CDs, nor does it include a USB cable to attach it to your computer. The DualPre device does not require any drivers, either, which is a nice bonus.

If your USB device requires bus power, and provides phantom power to microphones, ensure the device is connected directly to a USB port on the system. You are free to use a USB hub if it is powered, but that eliminates portability for some users. The DualPre can be powered by a 9V battery, and save some notebook battery life while on the road.

For FireWire devices, the connection scheme is fairly obvious, until you start requiring more devices on the FireWire chain. Make sure to put the device that you power on/off the least closest to the computer in the chain. For example, a MOTU Traveler connected to the computer and an external HDD connected to the Traveler would require the Traveler to be powered on in order for Mac OS X to mount the HDD. If this is inconvenient for you, then swap the connections so that the HDD is attached directly to the computer (and left powered on), and the Traveler attached to the HDD.

Sample Rate and Bit Depth

For the majority of measurements, you can safely stick with 44kHz 16-bit audio. These settings will give you accurate results up to 20kHz.

If you wish to modify your device's settings, use the Audio MIDI Setup application that ships with Mac OS X. You can launch Audio MIDI Setup from FuzzMeasure by clicking the 'Configure...' button under either the playback or record device settings. Alternatively, navigate to /Applications/Utilities and launch Audio MIDI Setup from that folder.

Note the USB Audio Codec device selected in the 'Properties For' popup button, and the Format: settings in the 'Audio Input' and 'Audio Output' sections. These values default to 44100.0Hz with the DualPre device, and you may change them to 48kHz if you wish.

If your device supports higher depths other than 16bit, be sure to increase the value as high as you can. Higher bit depths will result in higher-quality measurements.

Some devices have their own configuration panels (or knobs) for modifying sample rate and bit depths. Please refer to your hardware's documentation for further details.

Connecting a Microphone

You should use a microphone with a flat frequency response to perform measurements with FuzzMeasure. This guide will not go into details about what microphone you should choose, so make sure to pick one that fits your budget and needs.

Measurement microphones typically have balanced XLR connectors, and require phantom power (provided by a preamplifier) to operate. If your USB device has XLR connectors, it likely also provides sufficient phantom power for measurement microphones.

If your audio device has a level adjustment knob, be sure to set it so that measurements will excite the FuzzMeasure level meter at a reasonably high level (but not to the point of clipping). Some audio devices have clipping meters built-in, so use those as your first line of defense for eliminating overdriven measurements.

Connecting a Speaker

To perform measurements of a speaker, or to make measurements in a room or large venue, you must hook your audio hardware into some kind of amplified sound source. This often means an outboard amplifier and speaker, or a powered set of monitors.

FuzzMeasure sends its stimulus signal out on a single channel, so you can only test one speaker at a time (this is the nature of the measurement technique being employed, and not a limitation of FuzzMeasure). Conveniently, this leaves a spare channel open for Device Correction on 2-channel devices.

If your audio device contains both a headphone and a line output, always choose the line output over the headphones. Also, make sure that you don't set the output level too high, as you risk damaging your ears or equipment. Always test measurements at a low volume (use your level knobs on your hardware for safety!) and adjust the level upwards from there.

Loopback Connections

To check how good your device's frequency response is, or to use Automatic Device Correction, you will have to attach a loopback cable to your device.

In the picture above, the red cable is connected from the 'Right' input connection to the 'Right' output jack on the back. To set up the measurement in FuzzMeasure, ensure you choose Channel 2 for both your input and output channels (ensuring device correction is turned off).

Note that the input level on the device is set to 0dB gain — some devices have a gain knob that works completely differently, and the lowest value actually silences the input, so you'll have to experiment a little with your particular device.

When you take a measurement in this mode, you should see a graph that is mostly flat across the spectrum. If the graph is noisy or contains unusual swings, make sure your level knobs are properly set up and your cables are hooked up properly. To produce the graph above, the Right Gain knob is set to 0dB, and the 'Mix' knob at the back should be turned all the way to the 'Computer' side. The 'Level' knob on the back was turned to approximately 4/10.

Automatic Device Correction

Audio hardware can exhibit imperfections in its own frequency and temporal response, contributing to the reporting of potentially inaccurate data. Not all uses require such precision in the frequency domain (such as room acoustics, which only require accuracy below 300Hz), but for those that do, it is advisable to employ automatic device correction to eliminate those imperfections.

Using the device correction feature also eliminates device delay in the time domain. USB devices exhibit the worst delay of all — sometimes hundreds of milliseconds. FuzzMeasure's device correction will ensure that correct delay times and distances are reported.

Applying device correction in FuzzMeasure requires a physical loopback connection on your device in addition to the microphone and loudspeaker connections.

Impedance Measurement

When performing electrical measurements of loudspeakers, you require an easily-built jig. The schematic is as follows.

Note that the Input of the jig is hooked into the output channel of your audio device, and the Output of the jig is hooked into the input channel of your audio device. The probes are connected to the terminals on the speaker (red goes to the positive terminal, black to negative).

The easiest and cheapest way to build this jig is by splitting an RCA video cable in half, then soldering the resistor and probe leads to the correct points. A picture of this setup is included in the FuzzMeasure manual.

RCA video cables can be found inside many DVD player and satellite receiver boxes. They go unused these days in favour of S-Video Component, and HDMI cables — you will find one easily, somewhere.

ART USB DualPre

The ART USB DualPre is an excellent low-cost USB device that will suit most portable and desktop Mac users. Its 48kHz sampling rate and high-quality preamplifiers make it an attractive option for FuzzMeasure users on a budget. The build quality of the DualPre is fantastic — solid extruded aluminum and high-quality jacks and knobs.

Buy your DualPre at Sweetwater.

M-Audio DMP3

The M-Audio DMP3 is a high-quality 2-channel microphone and instrument preamplifier. It works great with the built-in audio hardware on Macs, and comes in a very well-built aluminum case. It has two analog input meters, and a wide range of features that would be useful in situations outside of FuzzMeasure's use. I prefer this preamplifier to the lower-priced AudioBuddy mainly due to its input meters, but also for its wide frequency range which will support recording at higher sampling rates.

A lower-cost solution would be to use the ART USB DualPre without the USB connectivity. When it is powered with the supplied power adapter, it provides a bare-bones preamplifier solution that you can use with your built-in audio hardware.

Buy your DMP3 at Sweetwater.