Note that the device cannot be reconfigured while the Test button is pressed. Click the Test button again to stop testing and enable reconfiguration of the audio device.

Check that you can hear the signal coming from your output device to ensure the output channels are configured correctly.

Check that the signal is visible on the scope to ensure the input channels are configured correctly. LiveSPICE maps the digital signal maximum (0 dB) to 1 V. Therefore, if the peak of the signal is near 1 V, it is likely that your audio system will have clipping issues.

Use the Test button to ensure your device is working. The test mode captures the signal from the input channels, displays the waveform on the scope, and plays the signal to the output channels.

To configure your audio device, use the menu to select Simulate Audio Configuration .

Tutorial: RC low-pass filter

This tutorial will walk through using LiveSPICE to build and simulate a simple passive first-order RC low-pass filter.

This tutorial expects that you have already configured your audio device in LiveSPICE.

For some background on the filter circuit to be simulated, see the low-pass filter article on Wikipedia.

Building the circuit

The first step is to build the circuit we are going to simulate. To begin, select File New to create a new blank schematic.

Adding components

Next, we will begin adding the circuit components. To add a component, find the component in the Component Library and click it. Then, click on the schematic where you want to place an instance of that component. We're going to need the following components, all from the Generic group in the library, to build the filter:

An Input ; the input signal will come from this component, which is an ideal voltage source.

; the input signal will come from this component, which is an ideal voltage source. A Capacitor and a Resistor .

and a . A Speaker ; the output signal is measured as the voltage across this component.

; the output signal is measured as the voltage across this component. A Ground.

Arrange the components roughly as follows:

Parts for the RC low-pass filter.

If you need to move the components, select them and then click and drag them to move them. You can also use the arrow keys to rotate and flip the selected components.

Tips You can search the component library by typing the name of the component you are looking for in the Filter field at the top of the library.

field at the top of the library. Use the arrow keys to rotate and flip components while adding them to the schematic.

Wiring the components

Next, we need to wire the components together. Select the Wire component from the library (or press Ctrl+W). Adding wires is a little different from the rest of the components, to draw a wire between two points, click on one point, and drag to the other point. Draw wires to connect the components as follows:

RC low-pass filter wired up.

Tips Holding Ctrl will allow you to draw more than one wire without selecting the wire from the library each time.

will allow you to draw more than one wire without selecting the wire from the library each time. A red terminal indicates that the terminal is not connected. Make sure none of the terminals are red before continuing to the next step.

Setting component values

The next step is to edit the values of the resistor and capacitor to build the circuit that we want. Let's build a filter with a cutoff frequency near a D 3 (the D string on a guitar), which is 147 Hz. If we use a 1 µF capacitor, we need roughly a 1 kΩ resistor to achieve this. To change the value of the components in the circuit, select a component by clicking it. This will bring up the properties for this component. Edit the Capacitance and Resistance fields of the appropriate components by clicking on them and typing the value.

Tips You can use u in place of µ when entering a property value. Similarly, Ohm and Ω are interchangeable.

in place of when entering a property value. Similarly, and are interchangeable. While setting incorrect units explicitly for a property will result in an error, unit-less quantities are implicitly interpreted to have the units of the property you are setting.

Running the simulation

Verify that your circuit looks like the following:

Complete RC low-pass filter.

To run the simulation, select Simulate Simulate on the menu. If you have not yet configured your audio device, you will be prompted to do so now. The simulation should now be running!

Click on any of the wires in the schematic to place a Probe. Probes generate signal data from the simulation, which is displayed in the Scope.

RC low-pass filter simulation.

Using this information, we can verify that the qualitative behavior of the circuit matches our expectations for the circuit we designed:

Input (red) and output (green) signals after plucking the low E string (E 2 , 82 Hz) of a guitar. Plucking the low-E string of the guitar shows the higher harmonics filtered, and the gain of the circuit near unity. Input (red) and output (green) signals after plucking the D string (D 3 , 147 Hz) of a guitar. We selected the corner frequency of the circuit to be the frequency of this note, and we can indeed roughly see the expected gain of -3 dB (1/ 2 ). Input (red) and output (green) signals after plucking the high E string (E 4 , 330 Hz) of a guitar. Plucking the high-E string shows a gain significantly smaller than unity, as expected.