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SR1 Operation Manual 108
© 2014 Stanford Research Systems
2.4.1 Common Analyzer Features
Analyzer Input Selection
Most of the analyzers share common controls that select the analyzer input:
Source
Most analyzers take a single input source, either analog channel A or B or digital audio channel A or B.
Details of the analog input connections, such as connector, coupling, etc., are set on the Analog Inputs
Panel. Details of the Digital Audio Input connection are set on the "Digital I/O Panel" . Some analyzers,
such as dual-channel FFT, intrinsically take a pair of inputs as their input source. For these analyzers
the input source selection will be simply "Analog" or "Digital." Some FFT-based analyzers (Single
Channel FFT, THD, IMD) can also use as input the output of the time domain detector analyzer, allowing
these analyzers to examine the post notch-filtered noise and distortion signal.
Converter
For analog signals, SR1 offers a choice of two analog-to-digital converters, each optimized for different
measurements. The high-bandwidth (Hi BW) converter is a 16-bit converter operating at a fixed sampling
rate of 512 kHz. The high-resolution (Hi Res) converter is a 24-bit converter which operates at fixed
sampling rates of 128 kHz and 64 kHz and variable rates which can be synchronized with the digital
audio output or input signal to perform cross-domain measurements. (Selection of the Hi Res converter
sampling rate is made on the
Analog Inputs Panel .) Digital Audio inputs do not involve a choice of
converter and the converter field is fixed at "Dig. Aud."
Fs
The current analyzer sampling rate is displayed in the Fs field in the upper right of the analyzer panel.
The sampling rate is dependent on the source/converter combination. For analog inputs the sampling
rate is dependent on the converter selection as described above. For digital audio inputs, the sampling
rate depends on the sampling rate embedded in the digital audio input signal. Note that for dual-
connector digital audio inputs, the sampling rate shown is the logical sampling rate representing the
actual spacing of the digital audio samples rather than the physical sampling rate on each connector.
When To Use the Hi-Bandwidth and Hi-Resolution Converters
Use the Hi-Bandwidth Converter when....
The measurement requires a bandwidth greater than the maximum bandwidth of the Hi-Res converter
When making THD and THD+N measurements of ultra-low distortion devices (<100 dB). The Hi-
Bandwidth converter signal chain includes hardware notch filters and hardware post-filter gain to
provide the best dynamic range for THD and THD+N measurements.
Use the Hi-Resolution Converter when....
When making FFT measurements within the bandwidth of the Hi-Resolution converter. FFT
measurements made with the Hi-Resolution converter can have an up to a 15 dB lower noise floor
than equivalent measurements with the hi-bandwidth ADC.