Be sure to see the related article by Jamie entitled “Anatomy Of A System Measurement Rig: Probes, Preamps & Processors”
While it may be counter-intuitive, for 99.52367% (roughly speaking) of common applications, the signal quality that our system measurement/analyzer rigs require to produce good measurements is, by pro audio standards, not really that high - particularly when compared to the signal quality demanded for studio recording or even simple listening.
What we require from the signal transmission path in our measurement rigs is really quite humble.
Frequency Response - Flat (+/-.25 dB) throughout the measurement bandwidth - a spec that should be easily achievable from 20 Hz to 20 kHz by all levels of audio gear.
The biggest offenders here are unexpected filters, HPFs caused by wiring issues or faulty DC blocking and phantom isolation circuits, LPF’s from long transmission lines and poorly implemented anti-aliasing filters, and of course the random unintentionally inserted EQ filter (a frustratingly common occurrence when grabbing measurement signal feeds off of extra board and processor outputs.)
Generally, this can be checked by simply examining the heavily averaged spectrum (RTA) of a known spectrally flat pink noise source. Any major FR deviations will show themselves quickly.
Channel Consistency (in FR and Latency) - The requirement that the measurement signal channels have virtually the same response and latency (which is by far the norm) so that dual-channel system response measurements - made through the comparison of two signal channels - are not biased by any FR or Latency differences between the signal channels of the measurement rig.
A quick way to check this is by applying the exact same signal to both input channels (or all channels in the case of a multi-channel rig) and then performing transfer function (FR) and delay (IR) measurements between channels.
The FR should be flat in magnitude and phase (signifying no latency issues), and the delay between the channels should be zero.
It is possible that your delay measurement could show zero time offset, and yet the phase response shows some deflection from flat in the VHF - this occurs when the two channels are off by a factor of 1/2 sample due to uncorrected interlacing in the ADC (the ADC samples at 96 kHz and alternates between channels to produce two 48kHz signals - the driver should correct for this 1/2 sample latency offset)
An in-depth yet easy-to-understand discussion of wireless systems, how they operate, issues that can plague performance, and solutions that do the trick in the vast majority of situations.
