User manual SABINE THE DIGITAL DELAY ADVANTAGE

[. . . ] THE DIGITAL DELAY ADVANTAGE A guide to using Digital Delays Synchronize loudspeakers Eliminate comb filter distortion Align acoustic image Contents THE DIGITAL DELAY ADVANTAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 - Why Digital Delays?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Loudspeaker Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - How to Synchronize Your Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - Processing (or Group) Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] (See the Precedence Effect below. ) Comb Filter Distortion Many who took high school science may remember ripple tank experiments where waves are generated from two separate point sources. The waves from each source combine to form visible interference patterns. In some places, the wave crests and troughs are in phase so they combine to make a larger wave. In other places the crests are out of phase, so the crest of one wave source is canceled by the trough of the other. Ripple tank experiments show the interference patterns are strongest when the amplitude of the waves from each source is equal. A similar interference occurs in sound systems when a signal is delayed and mixed back into the original signal. These interference patterns are called COMB FILTERS because their frequency response plots look like the teeth of a comb (see Figs. There are a number of common situations that cause comb filters. For example, when the program is played through two loudspeakers, the loudspeaker that is farther away interferes with the closer loudspeaker. Comb filters are also created when a performer is picked up by two microphones, one closer than the other. You even introduce comb filters by mixing digital effects back into the "dry" signal at the mixer's effects loop. Fig. delayed signal (both signals have the same amplitude); max. delayed signal (delayed signal has 10 dB less amplitude; max. Reducing the amplitude of the delayed signal reduces the comb filters' effect. ! Calculating Comb Filter Frequencies The reinforcement and cancellation frequencies depend on the delay time (the time difference between the arrival time of the original signal and the delayed signal). The frequency of the first cancellation occurs at 1/(2 x t) Hz, where t = the delay time in seconds. The cancellations are separated by (1/ t) Hz. 3 shows how the comb filters change with the delay time. Fig. 3: Comb filters get closer as delay time increases. Comb Filter Amplitude If the original signal and the delayed signal are the same amplitude, the reinforced frequencies increase in amplitude by 6 dB, while the out-of-phase frequencies cancel completely to - dB. " Comb filters cause a lot of problems. The frequencies that are reinforced are prone to excite feedback, while the out-of-phase cancellations make the program sound thin and over equalized. Try this simple experiment to hear what comb filters do to your sound. Fig. 4: Comb filters noticeably affect your sound. Stack two identical full-range loudspeakers as shown in Fig. Carefully align the HF horns and wire the speakers in mono. [. . . ] Now your ears have the same directional information as your eyes, so the performance will sound more natural and exciting. The best seats in the house just got better. Their purpose is to add intelligibility and listening comfort to the first few rows nearest the stage by filling in the areas missed by the center clusters. to the front fills to take advantage of the Precedence Effect. [. . . ]