The ValhallaRoom GUI is divided into several sections. The sliders in the left part of the GUI represent the high level parameters, in that they have the most dramatic and immediate effects on the sound.
From left to right, the parameters are:
- MIX: The mix slider controls the balance of the dry input signal to the “wet” reverberated signal, expressed as a percentage. 0% represents a fully dry signal, 100% is fully wet. The Mix slider uses a sine/cosine crossfade, such that the signal is balanced in volume at all settings of Mix.
- PREDELAY: The standard predelay control, which delays the onset of the Early and Late reverberation. The delay time is expressed in milliseconds. Predelay is useful in establishing the “size” of the room, in that the first reflections won’t be heard until after the predelay time. It can be viewed as moving the “walls” of the space in and out. From a non-physical perspective, the Predelay control is used to add some “space” between the input signal and the onset of the reverb decay, which can add clarity to the source signal. In the olden days, tape echos were used to add 15 to 30 milliseconds of predelay to the input of a reverberation chamber or plate.
- DECAY: The high level decay control for the Late reverberation. The Decay control could also be labeled “RT60” which stands for the time (T) needed for the reverb (R) to decay to a level 1/1oooth of the initial level (-60 dB). The decay time is based on the mid frequencies – the Bass Mult and High Mult controls in the Late section are used to dial in the decay times at low and high frequencies, which will be explained in more detail later.
- HIGH CUT: Controls the cutoff frequency of a -12dB/oct lowpass filter, with the units measured in Hertz. The relatively steep slope of this filter creates a more “natural” sound in the high frequencies, which reflects the air and wall absorption found in real acoustic spaces. Setting this to a range between 3000 and 7500 Hz is optimal for most larger rooms, while higher settings of High Cut are useful for emulating chambers and plates, as well as the brighter sounds of many digital reverberators.
- DEPTH: Controls the balance between the Early and Late reverb sections, measured as a percentage. 0% represents a signal that is only from the Early Reverb, while 100% represents a signal that is all Late reverb. The Depth control uses a sine/cosine crossfade. In addition, a great deal of effort went into “normalizing” the levels of the Early and Late reverb sections, such that the output levels are balanced over virtually the whole Decay range. This control was called “Depth” as a tribute to some of the classic digital reverberators such as the Lexicon 224 and Eventide SP2016, which featured Depth controls that adjusted the balance between early and late reverberation. The effect simulates moving a microphone further away from the source, or (more accurately) controlling the mix between close mikes and room mikes. The Depth control could have been called the “Early/Late Mix” control, but I didn’t like how that looked in the UI.
In addition to the high level sliders, the left part of the GUI contains the Reverb Mode selector, which will be the subject of the next blog post.