Who is this document for?
This document is for Product Managers and Software Developers of plug-ins who are
interested in tighter integration with SSL 360. Specifically, sending meter data to UC1 and
the 360 ecosystem.
Executive Summary
Read Only VST3 Parameters offer the best way forward for integrating 3rd party metering
data with UC1 and SSL 360... and the changes required to implement these will be
straightforward for most 3rd party plug-in manufacturers. The PreSonus IGainReductionInfo
VST3 Extension offers an alternative way of sending metering.
Overview
SSL 360 Link is a plug-in that can host other plug-ins and integrate them into SSL’s 360
system, allowing them to be controlled from hardware such as the UC1 or the virtual 360
Plug-in Mixer. Mapping generic VST3 Parameters to 360 parameters can be achieved wholly
from the SSL side using any 3rd party plug-in, but to enhance integration it is desirable to also
show gain reduction meter data from hosted plug-ins across the 360 system, specifically
compressor/limiter gain reduction values, and gate/expander gain reduction values.
The PreSonus IGainReductionInfo interface (as already implemented by various 3rd party
plug-in manufacturers), provides SSL with a way to show gain reduction metering for plugins hosted in 360 Link.
However, there is a better way...
The drawback of this method is that only one gain reduction stream is available per plug-in
and therefore, if using a plug-in with compression and gate metering (as many popular
channel strips have), these cannot be individually shown on the appropriate UC1 5-segment
LED arrays.
After some investigation, we have found that Read Only VST3 Parameters offer a superior
way to send multiple lanes of metering data (e.g. one for compression activity, one for gate
activity) to 360 Link and subsequently UC1 hardware. Furthermore, the VST3 Parameters
method is very similar to that used by ProTools to receive gain reduction meter values via
AAX Parameters - so if a 3rd party plug-in is already doing the work needed for ProTools it
should be easy to also send the data to the Link Plug-in.
We recommend the inclusion of this scheme by plug-in manufacturers at the next
opportunity for the best customer experience of SSL controllers with 3rd party plug-ins.
Technical Details
Version 1.0 of the Link plug-in lists generic hosted parameters that can be mapped to 360
parameters, in a future version it will list available meter parameters in a similar way so they
can be assigned to meters and shown in the Link Plug-in, all 360 hardware and the 360 Plugin Mixer. Factory mappings will have the most appropriate meter pre-assigned.
There are two ways hosted plug-ins can send gain reduction meter data to the Link Plug-in:
via Read Only VST3 Parameters as suggested in the VST3 SDK by using the flag
Vst::ParameterInfo::kIsReadOnly, or by implementing the PreSonus IGainReductionInfo
VST3 Extension.
If using Read Only VST3 Parameters, the hosted plug-in should supply a 0 to 1 floating point
value where 0.0 represents no gain reduction and 1.0 represents a full-scale signal being
reduced to silence. The Link plug-in will use the calculation 20*log10(1 – parameterValue) to
obtain a dB value to display in any meters that use a dB scale.
Using IGainReductionInfo the Link Plug-in can simply call getGainReductionValueInDb() to
determine the current meter value in dB.
Whichever method is used, the hosted plug-in should apply any ballistics itself before
sending the values to the Link Plug-in.
The VST3 Parameters method is similar to that used by ProTools to receive gain reduction
meter values via AAX Parameters, so if a 3rd party plug-in is already doing the work needed
for ProTools it should be easy to also send the data to the Link Plug-in.
The IGainReductionInfo interface is used by Studio One and Reaper, so a 3rd party plug-in
that has already adopted this system would already be sending the same data to the Link
Plug-in.
The IGainReductionInfo interface has one distinct disadvantage, only one gain reduction
value is available per plug-in, while many VST3 Parameters could be used allowing, for
example, distinct compressor and gate values to be displayed on separate meters.
For reference: the VST3 SDK Parameters and Automation section describes sending meter
values via read only parameters using the kIsReadOnly flag. The PreSonus extensions repo
includes the ipslgainreduction.h header file and downloadable documentation.