M/S Continuum
User's guide

Introduction

M/S Continuum makes it possible to select any arbitrary setting between the L/R and M/S signal representations by extending the definition of mid-side encoding to a continuous interval.

The plugin can be used in two ways:

• In standalone mode, as a width-preserving panning effect, or a special modulation effect for spatially balanced sounds
• In paired mode, allowing other effects to operate anywhere between L/R and M/S modes, with modulation options available

In paired mode, using the LFO (or automation-based modulation) can enable complex manipulation of the wrapped audio effect’s stereo response. Combining with delays or delay-based effects gives rise to a special category of use cases.

To make the controls more intuitive for panning purposes, the plugin implements an inverted control scheme, where the 100% setting corresponds to the M/S -> L/R conversion, while the -100% setting will result in a L/R -> M/S transformation. This is reflected in the naming of the automation parameter (as well as in the -1 superscript on the control label, which is a common notation for inverse transforms).

M/S transformations and panning as a single unified concept

Naturally extending M/S transformations to the continuous domain yields an algorithm that follows the exact same principles found at the core of True Pan, our plugin for stereo field rotations.

That may be surprising in and of itself, but it goes further: the double interval between forward and reverse M/S transformations actually correspond exactly to “true panning” between pure left and right positions.

This makes M/S Continuum (together with True Pan) a fourth panning mode in addition to balance control, stereo panning and binaural panning - in the space of 2-channel options.

All panning methods bring unique features to the table, so the most suitable one can be selected in any given scenario. True panning builds on its audio engineering-focused feature of being a lossless transformation, whereas all the other panning methods can alter the stereo frequency response via constructive / destructive interference, or by directly utilizing filtering or convolution as part of their design (which also adds phase delays, or even mono phasing artifacts, resulting in unpredictable mono performance that varies from product to product).

On the flipside, the performance of true panning is tied more intimately to the input’s stereo characteristics. It would be an apt description to say that the input signal plays just as important a role in the panning process as the panning algorithm itself.

Fundamentals of true panning

True panning has some stark practical differences when compared to other panning modes, so having a good understanding of these differences can be vital for some uses of the plugin.

The exact panning effect directly depends on the stereo composition of the input signal. The following cases are given for M/S Continuum (and may not fully apply to other products using true panning). An actual real-world signal can be a mixture of the listed base cases.

Bringing M/S modes to other plugins

M/S Continuum offers a special way to combine with other effects: the complementary pair feature. This method requires no routing or dry / wet separation, keeping tracks neatly self-contained. Of course a bus-based approach is also an alternative, without using paired instances.

When modulation is involved, different methods may lead to different results, when the goal is to process wet signals of other audio effects. Using a bus-based approach provides a choice between pre- and post-processing (not to be confused with PRE and POST roles of paired instances on a single chain, which is the focus of this chapter).

Any number of effects can be sandwiched between two M/S Continuum instances specially set up to provide a temporary transformation, restoring the original L/R format at the end of the chain.

A convenience feature is provided to link two boundary M/S Continuum instances together. When linked, the second instance automatically reverses any transformation applied by the first one, even in the presence of automation or an active LFO. Using the grouping feature, up to 63 pairs can be set up (if necessary, more can be added via a manual process, but free-running LFO’s cannot be perfectly matched outside the grouping feature).

The second plugin instance will detect it if the first one gets removed (or bypassed), and will stop applying the reverse transform. Please note however, as with any DAW-level effect bypass change, there could be a click/pop sound.

Workflow aid: automatic mode selection

Group selection is the only extra step necessary to set up a complementary pair from scratch. PRE and POST modes are automatically assigned, if the PRE instance is added first, and the plugins are in standalone mode at the beginning, with no assigned groups.

Group status indicators

The group selection screen provides real-time feedback about both allocated and still available groups. Incomplete groups are highlighted to assist with setting up pairs, or to indicate problems such as missing plugins or erroneous group assigns.

Please note that group status indicators don’t provide information about:

• bypassed plugins
• over-occupancy: more than 1 PRE and POST member in a group
• causality violation: POST -> PRE ordering, or PRE and POST not being on the same chain

Enhancing delay-based effects

M/S Continuum is a versatile extension to delays, or delay-based effects (e.g. feedback delay pitch-shifters, slappy reverbs, etc.).

Adding M/S capability, exploring in-between settings

For delays that have included both L/R and M/S patches, it is now possible to explore their graded versions, tailoring the stereo image to best fit the project at hand. The same is true for plugins that haven’t previously had M/S mode support.

Slow panning / swirling

The simplest time-varying effect is to use a low-speed LFO to gradually move the delay response around. This preserves the character of the delay and any patterns emerging from its tap configuration.

Relating the LFO to delay taps

A prerequisite to more advanced techniques is to sync up the LFO with delay tap timings, to have them both roughly on the same timescale. This is usually very straightforward in case of tempo-synced taps, given that tempo syncing is also available in M/S Continuum.

When the delay tap and LFO cycle times are more or less matched, strong interactions between M/S Continuum and the delay will result in new stereo patterns.

From that starting point, things can be varied quite a bit by exploring double, dotted, half or even triplet variants of the nominal rate, but larger differences can also give rise to interesting pattern variations.

In these setups, the LFO phase offset can be a crucial adjustment tool and have major effects on the resulting pattern.

Lessening a “clockwork-like” quality by adding variation

Tap configurations that work well in some cases may feel too mechanical and repetitious in others. A closely, but not exactly matched LFO setting can add some variation or increase pattern complexity to make the delay response feel more organic. Please note that changes to the stereo image are to be expected as well, as this base technique is part of several other techniques aimed at controlling the stereo image.

Widening or stereoizing

In a widening use case, modulation is added that moves together with the delay taps. If the modulation rate falls below a certain threshold, it can be picked up as a simple panning motion by listeners. The same thing might happen if the delay tap configuration is below a certain level of complexity.

Most mono delays can easily be turned into stereo ones with the LFO appropriately configured. Some stereo effects can be opened up and widened further, but that can vary from case to case.

“Stereoizing” delays can be useful even with sophisticated delay plugins. For example:

• A mono or narrow delay preset may have preferable characteristics that diminish when attempting to reconfigure it with stereo taps
• Decoupling position control from taps allows on-the-fly changes, or adding extra variation by using a non tempo-synced LFO (or a specially selected tempo-based rate that is not a trivial multiple of fraction).

Tightening L/R excursions without reducing width

Panned delays with pure L/R taps can sometimes result in an excessively “slappy” quality (even by panned delay standards). This happens when there is no overlap between panned echoes due the briefness of played notes, and/or the notes themselves having a strong, abrupt on-off quality in their ADSR envelope. Overlaps would normally create rich phase interactions, filling the space between the L - R extremes.

Another, highly technical characterization is that the delay cannot go from its transient phase to its stable one due to the lack of continuous input.

Following the same process that’s used for widening, namely setting up a co-moving modulation and exploring slight LFO rate variations and phase shifts, can also help with this kind of problem. Even without fine-tuning, the core effect is immediately apparent: a kind of spatial equalization, where directions that were left unpopulated by the L/R taps are filled in. This can also effectively remove “muddiness” in the mid channel / mono mix, but that may require fine tuning of the LFO phase offset or even the LFO rate.

During fine-tuning, a number of quite distinct pattern variations may be encountered. Mono monitoring is a highly efficient way to examine differences and make a choice, as long as stereo performance is also verified to be within expectations.

The impact of musical instruments / musical passages

To reiterate, while tap configuration is the one key factor in determining which combination techniques can improve or augment the effect, different kinds of sounds may also require different techniques or respond to processing differently. Example categories include:

• Smooth amplitude envelopes versus abrupt ones
• Legato versus staccato notes
• Wide versus narrow stereo images

Additional technical information

Pan law

M/S Continuum has an intrinsic, naturally emerging -3 dB pan law. It’s not manually configured or artificially added.
“True panning” doesn’t have any notions about the input signal’s position, for all it knows, by panning, it may actually restore an incoming pre-panned signal to the center position. To take this further, an input signal may be a combination of differently panned sounds whose relative positions will be preserved as each component is rotated to a new position - some of them away from the center, others towards it.

Usage as an actual mid-side encoder / decoder

Although the plugin’s real power lies in the continuous transform (as well as a number of additional features), at the min/max setting, it does indeed function as a plain mid-side encoder / decoder. If for some reason, this plugin is to be paired with a 3rd party M/S conversion tool, please note that the gain may need to be adjusted (by 3dB for typical M/S formats). This doesn’t apply to M/S-capable audio effects, as they are designed to connect to the L/R signal chain.