The combination of powerful DSP devices
with carefully designed algorithms allows multiple
and very precise equalisation.
The Shelving EQ settings allow for low and high frequency contouring, especially useful to tailor the system response to the acoustic environment. Roll-off frequencies as well as amplitudes are user selectable.
More refined and selective equalisation is available through the General EQ adjustments. Full control of three parametric EQ’s is provided, as well as Low and Hi Pass filters.
Presets are a very convenient way for defining a full set of EQ adjustments which encompass both Shelving and General EQ settings. The system comes with several factory presets, but the user is given the possibility for storing, recalling or editing new presets of his choice.
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Multiple
equalisation facilities
Once through the initial stage, the digital signal enters the main core of the active filtering system: the DSP. The selected device is a very powerful, specialised micro-processor, achieving 120 MIPS, with a large accumulator allowing double precision algorithms.
The choice of a DSP is not a trivial one as far as audio processing is concerned: a fixed point device has been prefered to a more versatile floating point one. The relevance of this choice has been confirmed by some recent paper showing that with careful programming and intelligent use of the double precision facility offered by fixed point DSP, these not only offered more processing power but were sonically performing better than their floating point counterparts, especially at low frequencies.
Digital audio processing algorithms can broadly be classified into two categories: recursive or IIR (for Infinite Impulse Response) filters, and non-recursive or FIR (for Finite Impulse Response) filters.
- Recursive filters are the most widely used in audio today. This is mostly because they simply mimic analogue filters, and as such their properties can be described by a few parameters, easily understandable and thus manageable by users: they are therefore well suited for general purpose processing units. They are also quite efficient in terms of processing power at low frequencies, but require careful and skilled programming to keep up with high sonic performance.
- FIR filters are a "different kind of animal" altogether, and on paper they have a lot to offer: capability to manipulate amplitude and phase in an independent way, rock solid stability, and unchallenged accuracy at high frequencies. However, they behave in a "global" way that cannot be pictured by a couple of parameters, and therefore allow very little flexibility. To put it another way, there are an extremely poweful tool for the system designer, but not for the sound engineer.
Inside the SM11 processing core, Focal have endeavoured to make the most of both worlds: a virtually unique combination of FIR filtering (for fine adjustments at high frequencies and phase manipulation capability), and IIR filtering (for efficiency at low frequencies and user friendly flexibility). Beside anything else, one of the beauty of digital processing is that it allows for a great deal of flexibility, through software changes. This is obviously a useful feature for a studio monitoring system, and the SM11 provides the user with an extensive set of possible adjustments.
Firtsly, tailored EQing is accessible with a combination of 3 fully programmable parametric Eqs, low frequency and high frequency shelvings, hi-pass and low-pass filters. The system response is therefore totally at hand to the engineer, allowing for any specific need required by the acoustic environment (location of the speakers with regard to nearby walls or reflecting surfaces, room resonances, etc·), or by subjective preferences dictated by whatever reason.
In this respect, a number of factory preset Eq settings are offered that will mimic the response of a typical cinema, or disco system, to name just a few. Those presets can be called, edited, and stored at leisure under other names.
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