dbx 160XT
A one-channel compressor/limiter that starts compressing at 7.8 millivolts and doesn't stop until it's inverting your dynamics.
Overview
The dbx 160XT is a single-channel compressor/limiter built around true RMS level detection. The first thing that jumps out of the manual is the threshold range: -40dBu (7.8mVrms) all the way up to +20dBu (7.8Vrms). That's a huge window. The 160XT can be triggered by a whisper of a signal, or it can be left alone to catch only the loudest transients in a hot mix. Owners report that this flexibility is the whole point. The unit rides a vocal gently and slams a drum bus just as readily.
The 160XT is the successor to the dbx 160X, and the manual is explicit about what was added: XLR-type input and output connectors, a balanced output that can drive a 600-ohm load to +24dBu, true power summing for stereo operation, and an input ground-lift switch for troubleshooting hum. The XLR connectors were added because the 3-pin connector had become the standard in professional applications. The balanced output gives common-mode rejection of noise like RF and 60Hz interference. The ground-lift switch disconnects pin 1 of the input XLR from circuit ground. It's the first thing to try when a ground loop is humming through the rack.
The compression controls are where the 160XT earns its reputation. The Threshold knob spans that full -40 to +20dBu range. The Compression Ratio control goes from 1:1 (no compression) through infinity:1 (output stays constant above threshold) and then keeps going into the INFINITY+ region, where the ratio goes negative. At -1:1, a 1dB increase in input above threshold produces a 1dB *decrease* in output. That's not a typo. The 160XT can invert program dynamics for special effects. The manual notes that the ratio potentiometer's control curve was designed with scale expansion at the subtle lower ratios, which makes fine adjustments easier and more repeatable.
The OverEasy switch selects between two compression characteristics. With it engaged, the 160XT uses dbx's OverEasy curve, where signals begin gradually activating the gain-change circuitry as they approach threshold instead of hitting a hard knee. The amber THRESHOLD LED lights when the signal is in that OverEasy region. With the switch out, the unit works as a hard-knee compressor/limiter, the classic behavior popularized by the original dbx 160, 161, and 162. The OverEasy mode is smoother and more transparent. Hard-knee mode is more aggressive and predictable.
The metering is unusually thorough for a single-channel unit. The upper row of 19 LEDs displays either input or output level, selectable with the Display switch. The lower row of 12 LEDs shows up to 40dB of gain reduction. The level display is factory-calibrated so that 0dB corresponds to +4dBu (1.23Vrms). A rear-panel Meter Calibration trimmer allows recalibration to any signal from -15dBu (138mVrms) to +10dBu (2.45Vrms), which helps in studios running at different nominal operating levels. The gain reduction LEDs don't reflect changes made with the Output Gain control, only actual compression.
The Output Gain control provides up to ±20dB of fixed gain in the output amplifier stage and does not interact with the threshold. So you can set your compression behavior first, then adjust makeup gain without throwing off the threshold calibration. The Bypass switch is a hard-wire bypass. It connects input directly to output, and the manual notes that audio will pass even if the unit is unplugged. An LED above the switch indicates bypass mode when AC power is present.
Stereo operation is handled through the Stereo Strapping jacks on the rear panel. A TRS cable between two 160XTs, or a 160XT and a 160X, allows the RMS detectors of both units to communicate, but only when one unit's Slave button is depressed. The slave unit sends its signal to the master, where the RMS power of both signals is combined to generate a single control voltage. Both channels then receive identical compression. The manual explains the reason: if two independent compressors process a stereo program, a loud sound in one channel causes gain reduction only in that channel, which shifts the perceived stereo image toward the uncompressed side. True power summing prevents phase cancellation between the two signals from causing unmusical compressor action. When strapped, only the master unit's controls need adjustment. The slave's front-panel functions (except Bypass and Display) are deactivated.
The detector input is a separate TRS jack of the normalling type. When a plug is inserted, the detector input is no longer connected in parallel with the audio input. This enables frequency-weighted compression. An equalizer inserted ahead of the detector but not in the audio path lets you alter the threshold response on a frequency-weighted basis without shifting the timbre or frequency response of the audio signal. The manual describes using this technique to separate vocals or instruments from a mix, or to prevent tape saturation when recording cymbals by boosting around 5kHz in the detector path so loud crashes trigger compression while gentle playing doesn't.
The 160XT has no power switch. The manual recommends leaving it on at all times, noting that power consumption is low, and suggests unplugging it only during extended periods of non-use. Units were shipped for 115V or 230V, 50 or 60Hz operation, and the rear panel indicates the specific voltage. The manual warns that connecting to an inappropriate power source can cause damage not covered by warranty.
EQ Magazine (April 1992, p.82) noted that the dbx 160X — the 160XT's predecessor — continued to be a professional favorite, particularly for its intelligent auto functionality. That reputation carried forward to the 160XT, which maintained the performance and ease of operation of the 160X while adding the professional connectivity and stereo-linking improvements.
The 160XT is a single-purpose dynamics processor, not a multi-band processor or a channel strip. It has an unusually wide threshold range, true RMS detection, and can go from transparent gain riding to full dynamics inversion. The 19-segment display, the hard-wire bypass, and the stereo strapping make it usable in both studio and live work.
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