The GML Model 8900 Dynamic Range Controller is the result of 22 years of research, prototyping, and limited manufacturing. The unit combines highly accurate log converters, true RMS detectors and other modern analog processing techniques in a stable “feed-forward” topology.
This unit reflects significant improvements in at least three areas:
- Distortion reduction in the signal level determination processor.
- Improved smoothness of the “soft knee” transition generator.
- Increased transparency and low-level performance of the VCA circuitry.
In addition, the units design fully exploits modern analog processing elements, and surface-mount construction to offer unprecedented accuracy, reliability, and calibration stability
The GML Model 8900 Dynamic Range Controller was intrinsically developed to react to loudness (rather than voltage) like our ears do. The GML Model 8900’s psycho-acoustic approach uses multiple true-RMS detectors, remarkably accurate log converters, and fast peak detectors to respond intelligently to real signal energy, not just electrical level.
This innovative design employs unique controls like Crest Factor, Timing, and Release Hysteresis to precisely control the dynamic features of musical performances; one would ordinarily change out the entire unit to gain this flexibility.
Familiar features such as Stereo Link, Soft/Hard Knee, Ratio, Output Level, as well as the comprehensive 40-segment tricolor Gain/Loss metering have been carefully optimized for flexible, creative control over a wide dynamic range with a noticeable lack of audible artifacts.
A Side Chain Input permits external frequency shaping to be introduced into the detection circuitry. The entire audio path is all-discrete, including the custom-built VCA, for unsurpassed transparency and low-level resolution. The GML Model 8900 is a 2U, two-channel unit which requires one 9015 power supply.
In contrast to most conventional dynamic range devices, the GML Model 8900 is a complex dynamic range controller which incorporates several powerful features to provide unparalleled flexibility and musicality. Indeed, the GML Model 8900 may be thought of as two completely different dynamic range controllers in one package: the simple (physically) change of the Ratio setting from Soft Knee to Hard Knee style compression affects this complete change in the unit.
All input signals, whether in Soft Knee or Hard Knee operation, must first undergo conversion to a logarithmic control signal. Logarithmic control, whether peak or RMS, results in the same audible effect–in terms of sonic coloration–over the entire range of compression, in contrast to contemporary dynamic range devices (which produce different audible artifacts varying with the amount of compression employed due to a linear control path signal). In the case of Sidechain operation, this logarithmic control signal is derived from the sidechain signal instead of the audio input signal itself, as in normal operation.
The logarithmic control signal generated by the log converter passes next to the GML Model 8900’s three detectors. These independent detection circuits are optimized to affect different transient aspects of any possible audio signal: the Slow RMS Detector acts on the least transient (program level) signals, the Fast RMS Detector responds to more highly transient signals, and the Peak Detector deals with the steepest transients. This control architecture allows for individual circuit optimization in each style of detector, in contrast to more traditional single-detector methods employed in most other dynamic range devices which often exhibit weaknesses in dealing with highly transient musical content. The nature of utilizing RMS-style control signals more closely follows the natural response of the human ear-brain complex, thus resulting in greater musicality and audible integrity, even in cases of drastic compression.
The Timing control affects the actions of the detection circuits in an intuitive manner, wherein interrelated attack and release time constants are varied simultaneously for the Slow and Fast RMS Detectors, while timing release values are determined for the Peak Detector. Interestingly, the release of the Fast RMS Detector corresponds to the attack of the Slow RMS Detector, while the Slow RMS Detector’s release time may be varied independently of its associated attack time constant by engaging the Release Hysteresis control.
