Metric Halo SpectraFoo - Manual (Page 56)

The Transfer Function
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Figure 4.2: Transfer Function of a Room Response with a time delay
• The data in the relative power display is invalid because the source and response signal are not time
aligned and therefore not really correlated with each other.
• A jagged, sawtooth wave-like trace in the phase response display indicates that the source and response
signals are not time aligned.
SpectraFoo provides a delay detection feature that is accessed via the “Compute Delay…” button present in the
Transfer Function window. The Delay Finder records a segment of both signals and computes the correlation
of the signals with each other. By moving the cursor to the largest correlation of the two signals, you set the
system delay and compensate for the measurement delay, time–aligning the two signals. Now the transfer
function measurements will be accurate.
The Delay Finder uses the Fourier deconvolution theorem to compute the impulse response of the signal pro-
cessing elements that the response signal has passed through. The deconvolution theorem allows SpectraFoo
to, in essence, “divide” the stimulation signal out of the response signal and create the impulse response of
the signal processing system being measured. The impulse response is the signal that we would measure if we
stimulated the system with an impulse (e.g. a loud, sharp snap).