Basic Input Operation - Your First Input Signal

When Daqarta first starts up, the Generator control dialog is visible. To replace that with the Input dialog, click on the small thin button under the toolbar Input button, or just hit CTRL+I.

The Input On/Off button at the top of the dialog is a duplicate ot the toolbar Input button. Hitting either will activate the sound card to display input signals on the channels and lines selected below it.

Note: On Vista/7/8/10/11 systems, if the Input button is disabled when Daqarta starts (and the free trial period has not expired), it means that Windows reported that there is no input device. Plug a cable into Line In or Mic In and restart Daqarta.

Below Input On/Off are Left and Right channel toggle buttons. At least one of these must be selected for input operation to proceed.

In columns under the Left and Right buttons are the respective line select buttons. These are "radio" buttons: Only one may be selected in each column; selecting another button cancels the previous selection.

The line select buttons are labeled with names assigned to them by the sound card manufacturer. Select the line or lines that are appropriate for your first signal input test.

If you are going to be using a microphone, make sure it is plugged into the appropriate sound card jack... usually it will be marked with small microphone symbol, or it may just say 'Mic'. Sound card microphones are typically mono devices, so you only need to select the Left channel, and select the Mic line under it.

If you are going to use some other signal source, it should be connected to the Line input. Some sound cards call their Line inputs by other names. If you don't see a line select button marked Line, you might look at how the sound card connector is labeled and see if there is a matching button, such as Aux.

The Line input signal must also be what is known as line level, meaning the maximum level is no more than a few volts... one volt is typical. This is a "casual" audio industry standard, so most consumer audio equipment has this avaialable on its "Line Out" jacks. Most sound card Line inputs can tolerate voltages up to 12 or 15 volts without damage, but the signals would be very distorted.

Do not connect home stereo speaker outputs to Line inputs, since the voltages can be much higher. Lab-type signal generators and oscillators can also have high output levels; hopefully, if you have one of these you also can measure its level to make sure it is appropriate. Otherwise, set the external source level to minimum for now.

Below the line select buttons are level controls whose labels change to match the selected line, and below those are Master level controls which work in tandem with their respective line level controls. (Your particular sound card may not have separate Master controls.) Assuming that you have not calibrated your card yet, the values for these controls will be in "steps", with 0 the most-sensitive and increasing negative values for reduced sensitivity.

(Once your card is calibrated the small dB button will be enabled, which allows the level controls to work in dB.)

The default calibration is +/-1.000 volt full-scale on all lines. Before the card is calibrated, there is no way for Daqarta to know what the true range is for any selected line, or for any setting of the level controls, so the full-scale range (as shown on the Y axis) does not change with line or level.

With Input on and the proper Left or Right channel and line selected, you should see a representation of the input signal on the display. For now, make sure that the Spectrum and Sgram/PT buttons are not active, so you will be viewing the waveform. If it looks like a flat line, increase the line and Master levels (upward toward zero) as needed to see the waveform.

If you still don't see anything when both line and Master are at 0, you should check your connections and the level of your signal source. If you are using a microphone, you can shout or whistle directly into it. If you are using an external signal on Line In, slowly increase its level.

Further tips may be found under No Input Signal in the Troubleshooting section.

Note that sound cards only respond to AC (Alternating Current) signals, such as sound or vibration. They do not respond to DC (Direct Current) such as a battery voltage, or to slowly-changing voltages such as from sensors for temperature or atmospheric pressure. In general, the signal must have a frequency of at least several hertz, and 20 Hz or more is better. (One cycle per second equals one hertz, abbreviated Hz.)

(See DC Measurements And Outputs for ways to get true DC input response. Alternatively, you can use a voltage-to-frequency circuit to read DC values with the Frequency Counter using the Fcal feature. There is also a tricky way to measure DC voltages via momentary contact, which is discussed in detail under Full-Scale Range Calibration.)

Likewise, sound cards don't respond to signals much beyond the normal audio range of 20000 Hz (20 kHz). Until you are sure that things are working properly, you should probably confine your test signals to 18 kHz or less just to be sure. 1000 Hz is a good test frequency, which is in the range of a typical high whistled note.

(You can, however, build a simple Frequency Prescaler to measure much higher frequencies, MHz and beyond, with the Frequency Counter using the Fcal feature.)

You can use the PgUp and PgDn keys, or the little up-down arrow buttons above the Y axis, to change the display magnification. If you magnify too much, the waveform appears to be "clipped" (the positive and negative peaks are cut off), but that is strictly a display phenomenon. On the other hand, if you see a clipped waveform and reducing the magnification doesn't eliminate the clipping, then the signal is too large for the input range; reduce the range (more-negative step number) until the clipping stops, or reduce the signal level at the external source.

You may want to apply Trigger to the waveform display to get a stable trace. The Trigger Control dialog will allow you select the trigger channel and set a threshold Level and Slope for the start of the waveform. Daqarta will wait for that same phase on each successive display; if the input signal is steady, as from an oscillator or signal generator, it will appear to be stationary on the display.

The Trigger dialog will also allow you to set a Delay so that the display will show an event that happens before or after the trigger event.

When Input is active, the relevant Display Channel buttons will be enabled and shown in the appropriate channel and screen colors. You can use thes buttons to toggle off the view of a distracting channel, if you have more than one active. These buttons only control the display; they don't toggle the actual input channels like the Left and Right buttons in the Input dialog.

You can drag the solid and dotted vertical cursor lines horzontally over the display, and the cursor readouts below will report the values under each cursor, as well as the differences between them.

You can also toggle to Spectrum or Sgram/PT (Spectrogram / Pitch Track) views instead of the default waveform display.

On most sound cards, you can toggle Generator along with Input. (The toggle order doesn't matter.) You can thus create a stimulus or driving signal with the Generator, and view the response on the Input line. This not only simplifies frequency response measurements, it also allows you to extract responses that are buried in noise, via synchronous waveform averaging.

See also Basic Generator Operation - Your First Output Sound.