Prism
Operation Manual Issue 2.00
Page 8.14
In this case, the signal-to-noise ratio of the non-attenuating converter has been
reduced to 60dB by the application of 40ns P-P of audio-band jitter noise. This test
also can be done with an analogue distortion analyzer, although the precise result may
depend on the bandwidth of the analyser notch-filter. This test has the advantage that
it can show the frequency response of the jitter attenuation of the D/A converter in the
audio band. In this case, the trace is flat because there is no attenuation at any
frequency.
The above tests can also be applied to A/D converters by applying the DSA-1 jitter
generator to the reference input of the converter and an analogue fs/4 tone just below
clipping at the analogue input. If a digital FFT analyser is not available, the digital
product could be returned to analogue for analysis providing a known highly-jitter-
attenuating D/A converter is used.
The DSA-1 can generate a special audio waveform called Jtest, which was specifically
developed by Prism Sound to excite extremes of data jitter on a cable. It contains
principally an fs/4 tone, but the DC-level of the tone is very slightly altered every 192
samples to produce a square jitter modulation at fs/192 (250Hz at fs=48kHz) according
to the degree of intersymbol interference exhibited by the cable. The FFT result below
shows the same two D/A converters, but this time driven with the Jtest waveform. 40ns
P-P of DSA-1 cable-simulating jitter has been applied: