It has previously been mentioned that the whole chain must have a dynamic operating range better than 124 dB for a 25.6 kHz broadband analysis, and correspondingly better than 160 dB for a 6Hz narrowband analysis, in order to match the specifications of high-quality transducers.
The following examples compare the performance of the Dyn-X input channel to a standard 24-bit input channel. Note that the standard channel when set to a lower input range can, in theory, provide measurements of similar quality, but with a high risk of generating overloads. The maximum input is 7VRMS (10Vpeak) for the Dyn-X input channel and 5VRMS (7Vpeak) for the standard 24-bit input channel.
In Fig. 6 (left) the two channels are compared for a 1 kHz sine wave attenuated 60 dB (re. 7V) corresponding to a signal level of 7 mVRMS. FFT analysis in 25.6 kHz, 6400 lines, and Hanning weighting was used resulting in an effective noise bandwidth of 6 Hz. For the Dyn-X input channel noise and spurious components are below –160 dB, thus matching the performance of high-quality transducers. The noise floor of the standard 24-bit input channel is approx. 30 dB higher and distortion components are clearly visible indicating non-linearity in the ADC.
In Fig. 6 (right), a similar comparison is done, but now with the sine wave attenuated 150 dB (re. 7V) corresponding to a signal level of 0.22 µVRMS. The noise floor and the spurious components are below –160 dB for the Dyn-X input channel and the sine wave is easily detected. For the standard 24-bit input channel, the sine wave is buried in noise. Noise and distortion components from ADC nonlinearity are clearly visible in the standard channel.
In Fig. 7 the two channels are compared in the time domain for a 1 kHz sine wave attenuated 90 dB (re. 7V) corresponding to a signal level of 0.22 mVRMS. Again noise and distortion components are clearly visible in the standard 24-bit input channel.