Specifications

2.18

Applications Manual

Revision 1.11Prism Sound dScope Series III

3.2.5.1 Amplitude vs frequency

The Amplitude vs frequency tests are arranged in the following subsections, which correspond to the

equivalent subsections of the AES17 standard:

Frequency response

Maximum signal level vs frequency

3.2.5.1.1 Frequency response

Applies to:

EUTs with analogue or digital inputs and analogue or digital outputs.

Aim:

To measure the variation in the

EUT

's gain with applied frequency.

Method

The EUT is stimulated with a sine stimulus swept from 10Hz to the

upper band-edge frequency

third-octave steps. In order t

o prevent overload in systems that use emphasis, the frequency response

is measured at –20dBFS. Prior to measurement, the output of the EUT is passed through a band-

pass filter centred at the frequency of the stimulus, in case significant amounts of aliasing or noise are

present. The RMS output amplitude of the EUT is graphed against frequency, expressed in dB

relative to the RMS output amplitude at 997Hz.

3.2.5.1.2 Maximum signal level vs frequency

Applies to:

EUTs with analogue or digital inputs and analogue or digital outputs.

Aim:

To measure the maximum signal amplitude which can be handled by the

EUT

against

frequency.

Method

The measurement is made using a sinusoidal stimulus with adjustable frequency and amplitude. The

output of the EUT is monitored with a level meter and a notch-filter-based THD+N analyzer. The

analyzer includes a standard low-pass filter at the

upper band-edge frequency

The stimulus frequency is swept from 10 Hz to the upper band-edge frequency in octave steps, and at

each frequency the stimulus amplitude is adjusted so that the output is on the threshold of having

either >1% THD+N or >0.3dB amplitude compression. The maximum signal level for that frequency is

then measured as the RMS amplitude of the EUT output. The results for both channels are graphed

against frequency in either dBu or V (RMS) as specified by the operator.