One great advantage of swept-sine wave deconvolution over MLSSA’s minimum length sequence technique is that it can generate harmonic distortion data, something that MLSSA can only do in a somewhat clumsy spot frequency mode. FuzzMeasure uses an advanced mathematical technique called deconvolution to derive an impulse response from a fast sine sweep, which, again using a Fourier transform, can generate a variety of frequency domain data. That all changed however with the launch in 2004 of a neat little OS X app created by Chris Liscio called FuzzMeasure.
#FUZZMEASURE AND IR MAC#
Windows users were well catered for with MLSSA and a couple of later competitors, but we Mac users for a long time had to borrow a PC or, as I did for a while, buy a cheap and clunky laptop just for the electro-acoustic stuff.
The one thing however that time domain based acoustic measurement lacked during its first couple of decades was a Mac based app.
#FUZZMEASURE AND IR PC#
Suddenly, complex time domain based acoustic measurement was available to anybody with a PC and a couple of thousand dollars. The real sea-change occurred however when Douglas Rife took Stanley Lipshitz and John Vanderkooy’s Minimum Length Sequence technique and created a comprehensive DOS based acoustic analysis package, christened MLSSA (pronounced Melissa). The Time Delay Spectrometry technique devised by Richard Heyser was, for example, soon packaged up into the relatively affordable TEF acoustic measurement system. Time domain measurements were the beginning of the end for swept sine-wave techniques. It was as if somebody had photographed the dark side of the Moon. The resulting ‘waterfall’ plot, that illustrates how speakers go on ‘playing’ after an input signal has stopped, was a revelation. This could not only generate the speaker’s ‘steady state’ frequency response, but also its frequency response at any time after the impulse. One in particular, Laurie Fincham at KEF, realised that computers made possible recording a speaker’s response to a short impulse and then applying a Fourier transform to translate between time and frequency domains. The arrival of cost-effective computing power in the 1970s didn’t go unnoticed by loudspeaker engineers. First, it needs a large anechoic chamber to produce accurate results at low frequencies, and second, it reveals very little about a speaker’s time domain performance how well the speaker starts and stops in response to an input signal. For all its slightly Heath-Robinson appeal though, Brüel & Kjær style swept sine-wave measurement had, and has, two big problems. Once warmed-up, the Brüel & Kjær kit could spit out wonderfully intuitive and revealing swept sine-wave frequency response and distortion charts.
#FUZZMEASURE AND IR HOW TO#
One of the first things I learned was how to use a set of classic Brüel & Kjær acoustic measurement equipment comprising a measuring microphone, a combined oscillator/preamp/ analyser (one of these) and a paper chart recorder (like this). I’ve been measuring speaker performance ever since I washed-up at Mordant-Short in the early 1980s as a raw design graduate.
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