User manual

Audio Generator
4-6
AM700 Audio Measurement Set User Manual
Available waveforms include the following:
Sine. The most common waveform used in audio analysis. This waveform can be
used for testing frequency response, for example, where you measure sine-wave
amplitude at various frequencies. The sine wave signal is also the only one that can
be swept.
Tone Burst. This is a sine wave that is periodically switched on and off. Tone burst
parameters are: sine-wave frequency and amplitude, period (the number of cycles
during which the on/off condition repeats), and burst width (number of cycles).
Available in high resolution mode only (with the analog and the digital generators),
this waveform is used for testing audio compressors, PPM meter ballistics, and other
devices that must adapt to audio-level changes.
IMD (intermodulation distortion). An IMD signal consists of two sine waves of
specific amplitude (or amplitude ratio) at specific frequencies. The AM700 analog
and digital audio generators can produce both SMPTE and CCIF IMD signals. This
signal is not available in high bandwidth generator mode.
A SMPTE IMD signal consists of a variable high-frequency and a fixed low-
frequency tone. By definition, a SMPTE IMD signal contains a variable-frequency
sine wave at 7 kHz and a fixed-frequency sine wave at 60 Hz. The amplitude ratio
between the sine waves is 4. SMPTE IMD settable parameters include signal
amplitude, ratio (the voltage difference between the high and low tones), and
frequency. The SMPTE IMD signal is typically used with an audio analyzer to
measure intermodulation distortion. In SMPTE IMD measurements, the IMD signal
components are looked for in two sideband areas around the center frequency of
7 kHz. Any distortion components are the result of mixing of the of the two signals
to produce upper and lower sidebands near the center frequency.
CCIF IMD signals, like those of SMPTE IMD, consist of two frequencies. CCIF
tones are closely spaced and at a higher frequency than SMPTE tones. By definition,
the CCIF IMD signal has a center frequency of 13.5 kHz and a frequency spacing of
1,000 Hz. The amplitude ratio is generally 1:1. CCIF IMD parameters that can be
set include center frequency, frequency spacing, amplitude, and amplitude ratio.
With the CCIF IMD signal, the close spacing of the two frequency components
produces difference components that are located near 1 kHz. The sum components
are out of the measurement band. The IMD distortion components are looked for in
a band around the expected difference of the two signals.