FRONT OF HOUSE
INTERNAL AND EXTERNAL DSP OPTIONS | Kent Morris
Photo by Denisse Leon on Unsplash
Analog consoles simply brought in signals, manipulated them for the mix, and then sent them out to the world beyond. Any manipulation of the output for clarity or control was left to outboard processing, namely equalization and dynamic range dedicated rack units. Each box performed one job: graphic EQ, compression, delay, etc. The result was a bespoke rack of interconnected gear designed to take the various mixes and massage them for their intended destination, such as mains or monitors. The later advent of digital consoles internalized this procedure since the built-in Digital Signal Processing( DSP) had enough bandwidth and horsepower to replace dedicated boxes. However, as mixing evolved, the need for more DSP soon outstripped the internal engines and made separate digital“ DriveRack” combo boxes the norm.
The current need for manipulation of the outputs can be met either inside the mixer through internal DSP or outside the mixer with a DriveRack type device, depending on the situation. For a small church with one set of mains, a pair of subs, a lobby feed, and a couple of floor wedges, almost any current crop of mixer can carry the load without sacrificing quality. As with all digital things, mixers only possess so much“ horsepower” in the form of excess capacity in the chip-set beyond what is necessary to mix. If this“ headroom” is sufficient, then the delays for the under balcony speakers, the EQ for the monitors, the compression for the subs, and the limiting for the mains can be dialed-in on the board. However, when the mixer is taxed with ancillary work, it will“ throttle back” its mix performance parameters, such as frequency response, to compensate for the strain. In this case, stewardship is best served through a separate DSP box designed for the task.
Setting up the processing for each application starts with determining what needs to be accomplished and how best to achieve that goal. The majority of concern will center around alignment of timing, the folding of various components’ frequency response curves into a cohesive whole and controlling dynamics for the application. When the mains loudspeakers originate from different points in space, aligning their firing time is critical for proper system response.
Since we cannot go forward in time, only back, the process is focused on the most rearward speaker and then the others are delayed their firing to match. For example, if the under balcony fills are 60’ in front of the mains, we add roughly 54ms of delay to the fills to allow the energy from the mains to arrive in sync given the formula of. 889ms per foot of distance. Subwoofers on the floor can be delayed by roughly 12ms in this situation while flown subs need only be aligned with the mains if they have been properly deployed in the same plane. There are numerous“ tricks” used as well to tuck the subs in or make the delays seem to disappear as a unique source including use of the Haas Effect.
In addition to timing, frequency response falls under the DSP umbrella. Not all loudspeakers in the room need to run full-range. By reducing certain aspects of response, the system can be made more cohesive. From tilt curves to frequency shading, and tapering, there are a host of options available to blend the various responses into a smooth experience. For instance, it is common to bleed off high end response in the transition phase between horizontal cabinets and to notch frequencies
that exhibit unruly behavior in certain physical orientations.
Dynamics control is the art of bringing the softest and loudest portions of a speaker system into alignment as befits the application. Compression leaves signal strength alone until a marked threshold is crossed and the system pushes back against an uninhibited increase. The extent to which the push is applied is dependent on many factors, but the goal is to have the system respond in a lively, yet controlled manner. Finally, limiting sets a brick wall filter at the top of the level game to prevent damage to components and people.
Modern DSP is capable of turning a functional system into an excellent system. It is vital to the operation of any modern installation and is the centerpiece of the art of tuning the system for the room.
Kent Morris Kent Morris is a 47-year veteran of the AVL arena driven by passion for excellence tempered by the knowledge all technology is in a temporal state.
84 June 2026 Subscribe for Free...