Creating optional output tools

Another optional step in preparation, is to add a meter, and scope to the output stage of the design.

Meter

The meter can be added simply by selecting it from the module browser and dragging it onto the canvas, then connecting it to the interleave module which copies the input to a second channel for dual-mono playback.

Rebuffer and sink

In order to view our output signal on a graph like a scope, we first need to rebuffer the input block size to a larger block size so we’re able to view a larger window of the signal. We multiply the input block size by changing the outBlockSize parameter in the Rebuffer module to “-50” as a start, but this can be changed to view different window sizes. Then we connect a sink module to the output, and double click the module to view the signal in real time.

Periodic Function Generator

We use a PeriodicFunctionGen module as the initial audio source of our design. You may choose to use a Sine, triangle, square, saw or impulse waveform. We will learn how to remotely control the frequency in the next step. Lastly, we add a General Purpose Scaler. You may optionally route this to the output pin and run the design to hear the oscillator.

The Frequency Modulation Subsystem

Creating a second oscillator

At the top of the above figure, we’ve added a second PeriodicFunctionGen module which will be added to our “carrier frequency” designated by a DC Source module. The carrier frequency should be set to something in the audible range, like 440Hz, as it is our fundamental frequency. The “modulator” (the PeriodicFunctionGen module above) should be set to a low frequency to start, such as 10Hz, and the amplitude set to a whole number, like 4. When the output of these two modules are added together, the output frequency modulates 10 times per second, adding and subtracting the amplitude value to and from the carrier frequency. What we end up with is a frequency control that oscillates between 430Hz and 450Hz, 10 times per second. Next, we will use this value to control the frequency of the initial oscillator we created in step 1.

Note: For now, you can ignore the subsystem input pin, multiplier and multiplexor, as those will be relevant in step 4.

Using param set to control the main oscillator

To remotely control the oscillator from step 1, we use a ParamSet module. We do this by connecting the output from our FM subsystem to the input pin of ParamSet, and setting the modVar parameter in the Arguments tab to “Oscillator.freq” as it’s the name and parameter of the module we want to control.

The Envelope LFO Subsystem

Adding an Envelope Generator

The initial step taken in the example, is to create two paths for the signal. The first path passes through the subsystem unaffected. The second path makes use of an EnvelopeGenerator module. We use a multiplexor to effectively bypass the envelope as desired. Set the multiplexor to 1 (checked) to enable the envelope.

Using an Oscillator to trigger the envelope stages

In this example we want to control the “attack” and “release” stages of the envelope. Starting with a PeriodicFunctionGen module, we set it to output a square wave at 2 Hz with an amplitude of 1. This will be used to trigger the attack and release stages one time each per second. By using 2 LogicCompareConst modules, we can set one to output “true” if the oscillator equals 1, and the other to output “true” if the output equals 0. Next we route 2 ParamSet modules to the EnvelopeGenerator.startAttack and EnvelopeGenerator.startRelease parameters. We’ve initially set the attack times and release times to 5ms and 50ms respectively, but adjusting these values can yield interesting results!

Random Generator

We use a Random Generator module to output a decimal value between -1 and 1 at a frequency we determine. Since previously we set the envelope to trigger twice per second, we’ll also set the frequency of the Random Generator module to 2Hz. Then we multiply the decimal value by 10 to get a decimal value between -9.999 and 9.999. Since we ultimately want to multiply the fundamental frequency of our oscillator by a positive whole number, we take the absolute value, then round to the nearest whole number. The Block Statistics module and Sink modules seen in the above figure are placed to aid in viewing the current generated value.

Connecting the pitch output to the Oscillator

Lastly, connect the output of the number generator to the frequency modulation (step 2) subsystem with a multiplexor to be able to toggle pitch randomization on or off.

Controlling a Second Order Filter

Begin by inserting a Second Order Filter module set to “VariableQLPF” in the signal path. Using the same technique as in Step 2, we remotely oscillate the cutoff frequency of the low pass filter between 200Hz and 5800Hz (3000Hz +/- 2800).

Filtering the delayed signal

After creating a simple bypass path, the delayed path is created by adding an Adder module, DelayMsec, then two Second Order Filters set to high shelf and low shelf. These are placed to created a filtered delay effect.

Creating a feedback wire

An error will occur if a wire feeds back in a system that has not been designated as a feedback wire. To do so, right click the wire feeding back and select “Make Wire Feedback”. Then fill in the corresponding data type of the wire, or other information as appropriate.

Creating the effect paths

First we create two paths for the input signal, one will go through a Reverb effect, and the other through an amp simulator. The Reverb path is given an additional path to flow into a Wet Dry module, which allows the user to turn a knob which determines how much of the affected signal is mixed into the unaffected or “dry” signal. Lastly we add a multiplexor to switch between the desired effects.

Importing FIR coefficients

For the last step in this application note, we import desired filter coefficients, or in this case presets for a Reverb and Amp Simulator effect. Do so by right clicking the FIR filter modules and importing an array of values.