SIAP creates time-constant reverberation – so that no pitch fluctuations, wow etc. can occur in the acoustic. Time-constant means that SIAP is inherently “piano-compatible”; the same is true for any other musical instrument and for the human voice. This contrary to systems which seek refuge to time variance, whereby the produced “reflections” are floating in time around a basic pitch (continuously changing pitch). Herewith a larger number of reflections is suggested than there in reality are; the main purpose of time variation is to limit acoustic feedback in order to prevent the system becoming unstable (howl round). Time variance leads to a howling decay of instrument strings (audible interference with the natural string sound decay) and to a blurry reverberation sound. Furthermore the shape and dimensions of the hall are continuously changing during while the music plays. These are highly undesirable artefacts of such processes. Of course in a natural acoustic the sound reflections do not have variable, on the contrary they have constant delay times, determined by the shape of the hall (length, width, height, diffusing surfaces, decoration, sound absorption of the materials etc.). As SIAP is time-constant, the system preserves the clarity and definition of the sound that is characteristic for good concert halls. And there is no risk of floating pitch decays of – for example – piano strings which have their own decay behavior. Self-evidently SIAP has sounds natural for people with “absolute-pitch-hearing”. For pianists, piano tuners etc. SIAP does not have to be switched off. For these obvious reasons no time-variation is present in a natural acoustic. Musicians and other critical listeners appear to be very sensitive for this.