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Volume Envelopes

WaveBoy has a number of internal volume envelopes which can be used in replacement or in addition to an external envelope and VCA. Due to the nature of how the volume is calculated, they have a more chiptune sound as compared to using an analog VCA.

While currently only volume envelopes are supported, the envelopes themselves were written so that they may eventually be used for other modulation destinations (e.g. pitch, or using the Step output for using envelopes for other modules).

Envelopes currently operate over wave and noise modes.

Usage

To configure a volume envelope, from the Main Menu, navigate to Volume Env by turning the left knob. Press the right knob when on Volume Env to bring up the Volume Env menu. Here you can use the left knob to select the Envelope or the Mode. An arrow (>) indicates which mode is selected.

Turning the right knob adjusts the selected setting. For envelope, it will cycle through the available envelopes. For mode, it will switch between the attenuation modes.

Each envelope has its own settings. To access those settings, first select the desired envelope and them press the right knob. To return to the volume menu, press the left knob.

To return to the main menu, press and hold the left knob while on the Volume menu.

Triggering the Envelopes

The Gate input is used to trigger an envelope and, where relevant, can be used for sustain.

Note that the gate will continue to be used for other functions while being used for envelopes.

Speed and Multiplier

Currently all envelopes have one or more speed parameters. This controls how fast the envelope changes the volume. Higher values mean faster speeds.

Additionally there is a Multiplier value. Higher values also increase speed at the cost of granularity. This is how you can create super snappy envelopes.

Envelopes

None

This is the default mode. There are no internal adjustments to volume such that any volume modulation will need to be done externally (e.g. via an envelope and VCA).

Decay

A simple linear decay envelope with only a speed parameter. When triggered it will go from full volume to zero and stay there until re-triggered.

A simple linear Attack/Delay envelope with separate attack and decay speeds.

ADSR Envelope

A full Attack/Decay/Sustain/Release envelope.

Modes

As of WaveBoy 0.59, there are now two modes. The original mode, called "Retro", uses an integer based addition and subtraction for volume scaling. This is very simple but produces artifacts. These artifacts tend to give a sort of high passed sound as the volume is lowered.

The new mode, called "Modern", uses floating point multiplication and properly scales the wave without introducing artifacts (to the limits of the 12-bit DAC anyway).

Saving Settings

The volume settings are automatically saved when leaving the menu (by press-and-holding the left knob).

Implementation Details

This information isn't needed just to use the envelopes, but is here for the curious.

The envelopes internally use a 16-bit range. This is so they can eventually be used for other sources (e.g. pitch). The volume range is only 8-bit. The envelopes values are logically shifted down to 8-bits as part of the volume interrupt routing.

These 8-bits are then used in a log lookup table which returns an 11-bit value. This is to smooth out the volume since volume is logarithmic.

It is 11-bits vs 12-bits (which is the actual bit-depth of the DAC) because the output is bipolar. The attenuated (inverse) value of the volume is subtracted from positive parts of the wave and added to negative parts (pushing either side towards the center).

The weight parameter for the envelopes increases the count step when the volume interrupt fires. Since the envelopes are 16-bit internally, snappy envelopes would require a very fast timer and would impact the range of slower envelopes. The weight thus allows the user to decide and keeps the timer period within a reasonable range.