2500+ Stereo Bus Compressor OPERATOR’S MANUAL Written for Automated Processes Incorporated by Dan Pfeifer Rev.
©2019 8301 Patuxent Range Road Jessup, MD 20794 USA 301-776-7879 http://www.apiaudio.
Table of Contents About This Manual ...................................................................................... 4 Important Safety Instructions .................................................................... 5 1.0 Introduction ......................................................................................... 6 1.1 Features ..................................................................................................... 6 2.0 Quick Start............................................
About This Manual This manual explains the operation and applications of the API 2500+ Stereo Bus Compressor. This manual is organized in sections that correspond to the front panel controls and rear panel interface.
Important Safety Instructions 1. Please read these instructions 2. Keep this information in a safe place 3. Do not use this device near water 4. Clean only with a dry cloth 5. Do not block any ventilation openings 6. Do not install near any heat sources such as radiators, heat registers, stoves, or other devices that produce heat 7. Do not defeat the safety purpose of the polarized or grounding type AC plug 8. Protect the AC power cord from being walked on or pinched 9.
1.0 Introduction Thank you for choosing the API 2500+ Stereo Bus Compressor. The 2500+ Bus Compressor is API’s flagship compressor that provides the unmistakable sound of API’s compression technology combined with unmatched parametric control. The result is one of the world’s best sounding and versatile stereo bus compressors that’s capable of handling an infinite number of production applications.
When many compressors are linked to the "STEREO LINK" mode, only one channel is controlling the compression. When the 2500+ is linked, the control voltages are summed together, but both channels are still detecting their own control voltages. This also eliminates changing of the tone of the compressor when linking is used. Many popular units actually change when linked! Additionally, each channel uses multiple VCA's to minimize noise and distortion found in single VCA compressors.
3.0 Overview The 2500+ Bus Compressor provides a comprehensive suite of controls: • THRESH (Threshold): The level at which compression begins (+20dBu to -20dBu) • Threshold LED: Indicates when the input audio crosses the selected threshold level • RATIO: The amount of compression applied after threshold o 1.5:1, 2:1, 3:1, 4:1, 6:1, 10:1, and ∞:1 • ATTACK: The time it takes for the compressor to respond o .03, .1, .
4.0 Compressor Section The COMPRESSOR section of the 2500+ sets the basic compression parameters for both the Left and Right channels. 4.1 Compressor Section Controls 4.1.
4.1.2 ATTACK ATTACK: Sets the time it takes the compressor to react when the level exceeds the set THRESHOLD • Fixed attack times: .03, .1, .3, 1, 3, 10, and 30 milliseconds (m/sec) 4.1.3 RATIO RATIO: Sets the ratio of input vs. output levels for signals that fall above the set THRESHOLD • Fixed ratios: 1.5:1, 2:1, 3:1, 4:1, 6:1, 10:1, and ∞:1 (x:1) • Compression with ratios of 10:1 or greater is generally considered to be limiting 4.1.
5.0 Tone Section The TONE section of the 2500+ controls the shape of the response curve at the onset of compression (KNEE), inserts the patented THRUST® filter before the detector, and set the detector path routing (TYPE). These controls all influence the tonal characteristics the compression applies to the audio. 5.1 Tone Section Controls 5.1.1 KNEE The KNEE function determines the shape of the 2500+’s response curve when the input audio crosses the THRESHOLD.
HARD: Sharp response curve • Immediate onset of compression (sudden transition to set ratio) • More aggressive and noticeable • The red LED illuminates when engaged MED • • • (Medium): Slightly rounded response curve Moderate onset of compression (firm, but less sudden transition to set ratio) Less aggressive and but still noticeable The yellow LED illuminates when engaged 2500+ Bus Compressor 12 API
SOFT: Rounded response curve • Gradual onset of compression (fade-in up to the set ratio) • Similar to an “over-easy” type knee • More transparent • The green LED illuminates when engaged 5.1.2 THRUST® The 2500+ includes API’s patented THRUST® circuit that can be switched in or out as needed. This places the THRUST® filter before the RMS detector that decreases the compressor’s reaction to low frequency content.
based upon those louder low frequencies, resulting in a control voltage that favors the low frequencies of the signal, causing pumping and a loss of punch. Sometimes, this is not desirable. By engaging the THRUST® switch, this inverse filter is placed in front of the RMS detector, evening out the energy by lowering the energy in the low frequencies and increasing the energy in the high frequencies, so each octave has the same energy instead of each octave having half the energy as the one lower.
NEW (Feed-Forward) In a feed-forward compressor, the RMS detector normally gets its signal from a split of the input signal. (The detector path can alternately get its signal from a SIDE CHAIN input jack.) With this method, the RMS detector sends a signal to the VCA that is an exact ratio of the desired compression set by the RATIO control. This is how many new VCA based compressors work. This can yield more aggressive compression and a harder, more affected sound.
6.0 Link Section The LINK section of the 2500+ controls the amount each channel will influence the gain reduction of the opposite channel. This allows “center-image shifting” caused by differing amounts of gain reduction on each channel to be reduced or eliminated. Most stereo compressors only allow 100% linking between channels. The 2500+ allows for linking to start at IND (independent), where each channel operates as a separate compressor with 0% influence between channels.
6.1.2 Link Shape The speed of the control voltage link between the Left and Right channels is selected using the SHAPE switch.
7.0 Output Section The output section of the 2500+ controls make-up gain, input/output blending, and compressor IN/out and bypass functions. 7.1 Output Section Controls 7.1.1 Make-up Gain MANUAL make-up GAIN: Toggle to select manual or auto make-up gain • Disengages “auto” make-up gain • Engages the manual make-up GAIN pot The “auto” make-up GAIN function applies make-up gain based upon the settings of the RATIO and THRESHOLD controls.
7.1.2 Blend and Mix The output section of the 2500+ allows 100% of the compressed signal to be sent to the output, to be crossfaded with the input signal, or to be “blended” in parallel with the input signal.
The BYP (Bypass) switch is a relay hard-wired bypass that routes the signal directly from the INPUT XLR to the OUTPUT XLR, without going through any electronics. If the power fails to the 2500+, the BYP automatically engages, preventing any loss of signal during the power fault. BYP (Bypass): Toggle to engaged the hard-wired bypass • Illuminates in yellow when engaged NOTE: When the 2500+ is powered off, it is held in the bypass state.
8.0 Stereo VU Meters The Left and Right stereo VU meters can indicate gain reduction and the signal level at the INPUT and OUTPUT connectors. 8.1 VU Meter Controls 8.1.1 Stereo VU Meters The Left and Right stereo VU meters indicate the amount of gain reduction being applied, as well as the signal level at the INPUT and OUTPUT connectors. 0 VU is +4dBu.
8.1.2 VU Meter Source The METER switch selects gain reduction, output, or input levels to be displayed on the VU meters. It is a silent function and is isolated so the VU selection does not affect or load the signal in any way.
9.0 Side Chain Input The 2500+ provides access to the side chain to allow external keying of the gain reduction via the SIDE CHAIN input jack on the rear panel. SIDE CHAIN: Balanced, line-level input • ¼” TRS connector • Tip=+, Ring=-, Sleeve=ground NOTE: Only active when TYPE is set to NEW. When the TYPE control is set to NEW, the signal arriving at the INPUT connector is routed to the RMS detector via the SIDE CHAIN input jack.
10.0 Power Switch & Rear Panel Connections 10.1 Power Switch The power switch for the 2500+ is located on the right side of the front panel. Power: Toggle to power the 2500+ ON and off • Blue LED illuminates when powered ON 10.2 Rear Panel The rear panel of the 2500+ provides the Left and Right audio input, output, and side chain connections, as well as AC power connections, voltage selection, and fuse. 10.2.
10.2.2 AC Power The AC power connection, fuse, and voltage selection switch is located on the rear panel of the 2500+. 115/230V~: Voltage selection switch Fuse: 0.5A/0.
APPENDIX A1 Specifications and Block Diagram A2 Recall Chart A3 API Limited Warranty and Service 2500+ Bus Compressor 26 API
A1 Specifications and Block Diagram 2500+ Bus Compressor 27 API
A2 Recall Chart 2500+ Bus Compressor 28 API
A3 API Limited Warranty and Service a. Warranty Information: This product carries a one year labor and a five year parts warranty from date of purchase. API (Automated Processes, Incorporated) does not cover claims for damage due to alteration and/or abuse. This warranty is limited to failures during normal use, which are due to defects in material or workmanship.
Dan Pfeifer is a Professor of Recording Industry at Middle Tennessee State University 2500+ Bus Compressor 30 API
8301 Patuxent Range Road Jessup, MD 20794 USA 301-776-7879 http://www.apiaudio.
