DAC Output Block Diagram

The QA402 DAC path is shown below. There are five types of signals that can be generated:

Sines. This can be one or two sines, with full independent control on each (frequency and amplitude)

Multitone Sines. This can be a user-selected number of sines per octave. Multitone is useful for looking at amplifier linearity. You can specify the number of tones per octave and the overall amplitude (in RMS) of the generated sines.

White Noise. White noise can be useful for testing the frequency response of acoustic elements in non-anechoic chambers. You can specify the RMS of the generated noise in a 20 to 20 kHz bandwidth.

Exponential Chirp. An expo chirp is useful for quickly testing frequency response. You can specify the amplitude of the swept signal.

User Provided. This is a pair of Base64 encoded strings representing left and right channel data as part of the REST interface.

As the block diagram shows, the input to the DAC can be sourced from one of five inputs (with one of the inputs being "ground" which will send all-zeros to the DAC.

The output of the DAC then passes through a 4 step attenuator with either 0, 10, 20 or 30 dB of attenuation. The DAC output level and attenuator setting are determined internally. The post attenuator amplifiers generate the signals that are fed to the output BNC connectors.

The mux settings can be controlled from the front panel of the Analyzer or via the REST command HTTP PUT /Settings/OutputSource/.