The SPL 9629 De-Esser is a 2-channel sibilance-removal unit, and it is a highly specialized audio tool for removing undesired sibilant frequencies without compromising the timbre and natural character of a voice. To solve this difficult problem, SPL has developed a circuit that is designed to combine a high level of technical performance with ease of use to create natural sound characteristics in recordings and live performances.

Traditional de-essers use compression techniques. In addition to the threshold parameter used to set the processing level, there is a frequency controller for setting the center frequency of the process (with bandwidths generally up to 4 kHz). Processing therefore compresses the entire selected range, not just the sibilant or S sounds. This results in the familiar and undesired side-effects such as lisping and a nasal-sounding vocal, which is sort of an audio-type slurring of the original signal.

The SPL De-Esser does things differently and in a more discriminating fashion. It monitors the S-frequency spectrum and automatically detects the sibilant frequencies. The de-ess bandwidth is set so narrowly around the range of the sibilance that neighboring frequencies remain unaffected. Input processed via this frequency band is mixed back into the main signal phase-inverted so that only the S-sounds are cancelled where the S-reduction controller determines the amount of de-essing in the phase-cancelled mix. The SPL De-Esser is designed to give a more neutral, unobtrusive de-essing process. Even at high S-reduction values the de-essing has a minimal effect on the character and timbre of the voice or even an instrument.

Additionally, the De-Esser system doesn't just look for sibilance in a wide 'general sibilance' region of the spectrum. Instead, the user simply sets a front-panel switch to Male or Female to adjust for the vocal characteristics of male or female voices.

The 9629 is a 1 RU rackmountable unit, and it features two channels of de-ess processing. Each channel is outfitted with an S-REDUCTION potentiometer complimented with Auto Threshold, Male/Female and Active (on/bypass) switches, and an on/off power switch. Located on the rear of the 9629 are balanced XLR and jack plugs for the inputs and outputs and a GND lift and voltage-selector switch.

Function de-Essing
Number of Channels Two
Inputs 2 - XLR or 1/4" TRS
Outputs 2 - XLR or 1/4" TRS
Nominal Input Level +6 dB
Input Impedance 22 kOhms
Maximum Input Level +24 dBu
Maximum Output Level +22.4 dBu
Minimum Load Impedance 600 Ohms
Additional Features Relay hard bypass / power-failure safety
Frequency Response 20 Hz to 50 kHz (50 kHz = -3 dB)
Common Mode Rejection -80 dBu @ 1 kHz
Total Harmonic Distortion 0.002 % @ 1 kHz
Signal to Noise Ratio -93 dBu (CCIR 468-3) 
98 dBu (A-weighted)
Power Supply Toroidal transformer: 15 VA
Fuses 115 V (230 V) 630 mA (315 mA)
Voltage Options Voltage selection switch 115 V / 230 V with GND (ground) lift switch
Dimensions (W x H x D) Standard EIA 19" / 19 x 1.7 x 9.3" (IHE 482 x 44 x 237 mm)

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