/// <summary>
/// Triggers a note on event for the Helm instance(s) this points to.
/// Instead of a midi note, uses a frequency measured in hertz.
/// You must trigger a note off event later for this note by calling NoteOff.
/// </summary>
/// <param name="frequency">The frequency in hertz to play.</param>
/// <param name="velocity">How hard you hit the key. [0.0, 1.0]</param>
public void FrequencyOn(float frequency, float velocity = 1.0f)
{
int number = 0;
pressedFrequencies.TryGetValue(frequency, out number);
pressedFrequencies[frequency] = number + 1;
Native.HelmFrequencyOn(channel, frequency, velocity);
}