Data AcQuisition And Real-Time AnalysisScope - Spectrum - Spectrogram - Signal Generator
Software for Windows
Science with your Sound Card!
Contact us about
Input Line Selects
Macros: InLineL, InLineR
There are up to 8 line selects per channel, depending upon your sound card. If your card has less than 8 input lines, the unused buttons will be disabled and marked 'Unused'. If your card has more than 8 lines the rest are ignored here, though in a pinch you may be able to use the standard Windows mixer. (Not recommended.)
You may select only one line per channel at any given time; the rest are automatically deselected and muted to prevent spurious input signals. The level settings for the other lines are stored, though, so if you change selections the prior level is restored.
The lines are labeled with text provided by the card maker. There are no standards for this text, or for the order in which lines appear, and there is no programmatic way for Daqarta to tell them apart. However, there will almost always be a line marked 'Mic'. There is also usually one marked 'Line', though some cards call this 'Aux' when they don't have a separate Aux line.
Line and Aux will probably be the lines you will use most. These usually have similar specifications, and are designed to handle signals in the volt range.
Mic has a built-in preamp, so it is typically designed to handle signals in the millivolt range. (But see Note below.) This may or may not be useful, since many (if not most) sound card mic preamps are not of very high quality. In addition to high noise, they typically have built-in filtering to reduce high frequencies.
Besides the preamp quality, most sound card Mic inputs are mono. The Right channel of the connector is dedicated to providing "phantom power" to an electret mic. So, even if there are separate Left and Right Mic lines shown in the dialog, they are both connected to the same single input. The Mic may have separate Left and Right Level controls, but they just allow you to send different amounts of the same signal to each channel. Worse, the Left and Right Mic lines may interact when they are both active, such that one line loads down the other and upsets the calibration.
Most applications that need to work with low-level signals would benefit from using an external preamp connected to the Line or Aux inputs. Use Mic inputs with caution.
Despite all that, a Mic input can be perfectly adequate for some applications. If you are looking at low-frequency speech components, the built-in Mic filter may actually be helpful. And most evoked potential signals, for example, are essentially all noise anyway (they require synchronous averaging to see the evoked potential), so a little bit of added noise is insignificant. Plus, evoked potential preamps commonly filter the signal drastically anyway (100 to 3000 Hz is typical), so the Mic filter causes no problems at all.
Note: Some laptops that only have a Mic input jack may nevertheless auto-detect and support full-performance stereo Line inputs on that same jack. The Input dialog may continue to show only Mic, so you may need to experiment to see what is going on. You can use an ordinary male-male cable from the headphone output jack, and create a stereo test signal with the Generator. One simple approach is to load the Default.GEN setup, which has only the Left output producing a 440 Hz sine wave. Toggle the Right output on at the top of the dialog, then click on the Right Wave Controls button and toggle Stream On. Change the Wave type or Tone Frequency so that the two channels are easily distinguished when looking at the input waveforms.
You should be sure to calibrate all the lines you might ever want to use. It's easy to calibrate one more line when you are doing all the rest, but not so easy when you discover in the middle of an experiment that you need a line you never bothered to calibrate.
Note that many sound cards are "Mux" type, which means they only allow you to select one line at time. The problem is, that includes both channels. In that case, Daqarta disables the Right selects, and you will be forced to use Left and Right inputs of the same line. That's usually what you want anyway, so this is not generally a problem.
Also, Mux cards usually don't have a separate Master Level control.
Note that attempting to select a line that is disabled may cause the macro to be ignored, or to abort with an error message. If your card is a "Mux" type then all the Right line select buttons are disabled.
Macros must refer to Input lines by number, not by name. Line numbers start from 0.
InLineL=0 sets the Left Input to use line 0.
InLineR=2 sets the Right Input to use line 2.
See also Input Control Dialog
Questions? Comments? Contact us!We respond to ALL inquiries, typically within 24 hrs.
Over 30 Years of Innovative Instrumentation
© Copyright 2007 - 2020 by Interstellar Research
All rights reserved