ACMT - Applied Computer Music Technologies Ltd

ACM76SA Product Operating Guide
 
Access to plug-in parameters is provided by a fully resizable graphical user interface. Your host application may also provide access to parameter adjustments and additional configuration.
 

 
Graphical User Interface
 
The plug-in settings are adjusted by clicking and dragging on the rotary controls or buttons. Some controls may have detents – these manifest themselves as areas in the rotation where the reluctance to move is increased such that you have to drag them a bit harder. They are intended to behave similarly to real controls which may have a 'click stop' at 0dB for example.
 
You can also adjust the controls by placing the mouse pointer over them and using the scroll wheel. In this case the detent has no effect.
 
Control Modes
 
Clicking the preferences button opens the plug-in preferences panel to configure the control mode. The control mode determines the way in which the rotary controls respond to mouse movement. This may also be configured via the host application preferences where applicable. In all modes, double clicking the centre of a control will return it to its default position.

• Circular. In this mode, clicking on a control will move it immediately to the mouse pointer’s angular position. To adjust the control, drag the mouse pointer in a circle or an arc.
• Relative Circular (Default). This is the default mode unless changed by host application settings. Similar to circular mode, however moving the mouse will adjust the control relative to its current setting.
• Linear. In this mode, the control responds to vertical mouse movement. Drag up to increase the value, turning the control clockwise, or down to decrease the value, turning the control anticlockwise.

Multiple Switch Selection
 

Control Functions
 
In keeping with many vintage hardware designs, the front panel designations are often best viewed as a guide, rather than an accurate indication of specific control settings.
 
1. Input Gain Control
 
The Input control adjusts the signal level entering the plug-in. Similar to original hardware, this regulates the amount of signal reaching the input transformer and FET VCA stage, and will therefore also have an effect on the harmonic content generated by the plug-in.
 
2. Output Gain Control
 
Following the FET VCA stage, the Output control adjusts the amount of signal feeding the output amplifier stage and transformer. Typically this is used to make up for attenuation by the VCA resulting from the compressor action. As this control is placed before the final output stage, it will also have an effect on the harmonic content generated by the plug-in.
 
3. Attack Time
 
The Attack control sets the time taken for the compressor to respond to increases in signal level above the threshold, and turn down the VCA stage accordingly. The attack time is adjustable from approx 20us to 800us, with the fastest setting being in the clockwise position.
 
3a. GR Disable
 
In some original hardware, turning the Attack control fully anti-clockwise disconnects the side-chain, defeating the compressor action, while leaving the VCA and associated signal processing in circuit, providing some useful analogue character if required. In the plug-in this is emulated as a ‘push / pull switch’ which can be activated by holding down [ Shift ] and double-clicking the Attack control. A similar effect can also be achieved by deselecting all the ratio buttons or ‘all buttons off’ mode.
 
4. Release Time
 
The Release control sets the time taken for the compressor to recover after the signal drops below the threshold. The release time is adjustable from 50ms to 1.1 seconds, with the fastest setting being in the clockwise position.
 
5. Ratio Selector Switches
 
The four switches to the left of the VU meter select the compression ratio, the amount by which the output will increase for a given increase in input above the threshold. Similar to original hardware, the plug-in does not have a separate threshold control but instead this is determined by the ratio selection. Fine threshold control can be achieved by adjusting the input to the unit using the Input control.
 
In normal operation the ratio switches have an interlock provided by the plug-in GUI, which ensures only a single button can be activated at once, however in keeping with original hardware, it is possible to select multiple ratio switches at the same time if required. In this case, hold down [ Shift ] when clicking the corresponding ratio button. In this way, classic settings such as ‘all buttons in’ can be achieved (although, owing to the circuit operation, selecting 20:1 and 4:1 together will have the same effect). It is also possible to disconnect the side-chain altogether by selecting ‘all buttons off’. In this case the compressor action is defeated, however the VCA and associated processing remains in the signal path providing some useful harmonic colouration.
 
Double-clicking any of the ratio buttons also provides a useful shortcut for selecting ‘all buttons on’ mode.
 
When using automation within your chosen DAW application, be sure to enable automation for all four of the ratio selector switches to ensure correct operation.
 
NOTE: When selecting multiple ratio settings, including ‘all buttons’ mode, there may be a momentary increase in output level, as these modes affect the internal bias configuration of the circuit emulation, which may then take a short time to settle.
 
6. VU Meter
 
The VU meter indicates the amount of gain reduction taking place, or alternatively the output level from the effect, depending upon the meter mode selection [7].
 
7. Meter Mode
 
The switches to the right of the meter determine the meter mode:

• 7a. Select ‘GR’ to show the amount of gain reduction (the meter will normally show 0VU and reduce as the gain reduction increases).
• 7b. Select +4dB to show the output from the unit relative to +4dBu or
• 7c. Select +8dB to show the output from the unit relative to +8dBu.

NOTE: To provide a more usable range with typical signal levels encountered in the digital domain, the meter is calibrated to show 0VU for -18dBFS with the +4dB setting selected.
 
8. Effect In / Out
 
The bypass switch (labelled as ‘OFF’ on the front panel) places the compressor and its gain controls in or out of the signal path. With the switch off (not illuminated), the signal passes through unaffected by the compressor. With the switch on (illuminated) the compressor will begin affecting the signal.
 
NOTE: Selecting ‘all buttons off’ mode – or all ratio buttons deselected – can also be used to bypass the compressor action, by disconnecting the side-chain, however in this case the level controls, VCA and associated signal processing remain in circuit which means some analogue saturation or harmonic content will still be present.

ACM76SA Technical Specification
 
Product Specifications

• VST, VST3, AAX and CLAP plug-in.
• Windows & Linux compatible.
• Mono or stereo operation.
• Interpolated controls for smooth parameter changes with no 'zipper' noise.
• -18dBFS reference level for 0dBu.
• Frequency Response: 20Hz to 20kHz +/- 1dB.
• Maximum Gain: 45dB +/- 1dB.
• THD: 0.14% or better, measured at 1kHz, 0dBu, fast attack, slow release.
• Attack Time: 20us to 800us.
• Release Time: 50ms to 1.1 seconds.
• Compression Ratio: 4:1, 8:1, 12:1 and 20:1.
• Compression Threshold:

  Compression Ratio	Input at Min. Threshold
  4:1	-21dBu
  8:1	-19dBu
  12:1	-18dBu
  20:1	-14dBu

• Polarity invert switch.
• Output level trim (+/-6dB).

Please note: In the interest of continual product improvement, specifications may be subject to change without notice.

ACM76SA Download Free Demo
 
1. System Requirements - Windows

• 64bit Windows 7 or newer.
• A compatible host application.

2. System Requirements - Linux

• Linux x86-64/AMD64 64bit e.g. Ubuntu 20.04 LTS or newer.
• A Linux compatible host application.

3. Free Demo Limitations

• Every 60 seconds the plug-in will fade to silence momentarily. To remove this limitation you will need to have purchased a product activation code.
• To remove the demo limitations, open the plug-in in your host application and click the lock button at the top left of the plug-in GUI to open the license entry dialogue. Type (or paste) your product activation code into the text box. You will then need to restart your host application to complete the process.

4. Product Support

• All downloads include their own installer, manual, and installation instructions. Easy to install with just a few clicks.
• If you need help downloading or installing the software please contact product support for assistance.