User manual

Audio Generator
4-8
AM700 Audio Measurement Set User Manual
On playback, the contents of the audio source file are copied into a buffer and the
generator is set to play the signal from the buffer.
The data format is binary 32-bit long words, one long word for each audio sample
point. The AM700 uses the lower 24 bits of each word; the upper 8 bits are ignored.
Data must be in Motorola fractional audio format (each 24-bit number is expressed
as a fraction ranging from 1 to –1, or 7FFFFF to 800000). For details about the
Motorola fractional audio format, refer to Motorola documentation.
Once created, the user signal file is transferred to the AM700 by floppy disk. For
information about transferring files using the floppy disk drive, refer to Storage on
page 2-19 and to AM700 Storage Manager on page 4-132.
NOTE. In converting data from Motorola fractional audio format to volts, for
example, if you want the voltage to be calibrated, it must be scaled to place one or
more of the sample points at 7FFFFF or 800000.
NOTE. If you apply a user signal when the digital generator is not in Follow mode,
the volume control is inoperative, and the data is sent exactly as it appears in the
file. However, if the digital generator is set to follow the analog, when you apply an
analog user file, the volume can be controlled.
Multitone. This signal contains selected sets of sine-wave frequencies. The amplitude
of a multitone test signal is defined as the RMS value of the combined signal
frequencies (not the peak amplitude of any single frequency in the signal).
Multitone test signals are used to check audio-circuit frequency response, phase
response, and total harmonic distortion and noise levels. Multitone signal amplitude
can be specified using the Amplitude soft key in the Waveform Control display.
Refer to Multitone Files on page 4-9 for information on constructing a multitone
test signal.
NOTE. The overall signal-to-noise ratio of a multitone signal is lower than that of a
normal sine wave.