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DartDisk User Guide

Low-Noise Operation

Low-noise operation is important when acquiring low-level signals. The essential concept is

signal-to-noise ratio (S/N or SNR), which is the dB ratio of the input signal to the effective

input noise (EIN) of the Dart card. S/N should be maximized. When a signal's S/N falls

below 50-60 dB (depending on source material), the noise component becomes audible to

most human subjects.

EIN mathematically expresses the aggregate noise contribution of all internal noise sources,

referred to the device input. S/N is the ratio of input signal level to EIN. The principal Dart

noise sources are 1) input noise of the programmable gain amplifier and 2) effective noise of

the digitizer. Amplifier noise is about 12 uV-RMS or -98 dB re full-scale (1.4 Volts peak).

Digitizer noise is about 2 bits, which translates to –84 dB re full-scale or 60 uV-RMS.

Therefore at 0 dB programmable input gain, EIN will be dominated by digitizer noise, while

at gains > 20 dB, EIN will be dominated by amplifier noise. So EIN decreases as

programmable gain increases, and for optimal low-noise operation, use the maximum

input gain possible without saturating (clipping) the input signal.

Following are typical EIN values, measured at 0 dB and 19.5 dB programmable gain. EIN re

full-scale represents the card's maximum S/N capability at that gain setting. Nominal full-

scale voltage for the Dart is

±1.4 Volts.

Gain = 0 dB Gain = 19.5 dB

EIN (uVolts-RMS) 60 uV 12 uV

EIN (dB re full scale) -84 dB -98 dB

11. Using DartDisk and SIGNAL

DartDISK can be used in conjunction with the SIGNAL

sound analysis program to record

extended acoustic data sequences, then locate and analyze the sound events within them.

This section describes the overall approach, basic tools, and important information sources.

The two programs work together as follows:

• DartDisk provides long-duration high-frequency direct-to-disk recording, producing long

continuous sound files in the SIGNAL or Wave sound file format.

• SIGNAL can display the entire sound file (see below), which the researcher can use as a

roadmap to extract specific sound events. SIGNAL can manually extract, display,

measure, and analyze these events and store them as individual sound files. SIGNAL can

also be programmed to perform acoustic measurements automatically on the stored

events.

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