>@9
Multitone Audio Test System
User Manual
V 3.32
27 / 71
EXTernal
In case of expected clock frequency differences between the generator and analyzer the
user has to activate the EXT mode. Frequency shifts appear e.g. in combination with analog
tape recorders, where the recording and the playback speed are not identical, or due to local
separation of generator and analyzer. Up to 1s transmission time is allowed.
EXTNoheader
This mode may be used after transmission of several multitone burst transmissions in mode
EXT only. The analyzer synchronizes itself onto the SYNC blocks of these preceding
multitone bursts, before it eventually gathers the burst in mode EXTnoheader.
Gathering Data
After triggering and synchronization, the analyzer waits one period of the multitone burst to
let the transients of the DUT disappear before it starts with a two-block FFT. This calculation
takes - depending on the block length - between 48ms and 190ms. The analysis includes
•
Decoding of the bit stream to get two stereo signals
•
Windowing with Hanning window (where necessary)
•
Organization of bits (bit reverse organization of results)
•
Calculation of level and phase from the complex spectrum
The calculated vector is placed in the result area of the memory and the DSP is ready for the
next acquisition.
If the user queries for measurement results, the CPU reads these stored data from the
internal memory and computes the required results out of them. This process requires
considerable computations since all the bins have to be read, squared and summed up for
the results calculation. As soon as this process is finished, the results are transmitted and
thus available for further processing.
