Saturday, April 27, 2013

FM Acoustics 268-C Linearizer - How it works part 4

Fig. 6 Another great feature of the unique FM 268-C is that one is not limited to the five center frequencies! If a signal aberration at say 1000 Hz needs correction the FM 268-C allows to do this without resorting to any poor sounding parametric/state-variable filters or other musically non-satisfactory equal-izing circuits. By simply decreasing the subtraction at 3.2 kHz and increasing the subtraction at 800 Hz the center frequency now moves down to any frequency requested, in this case the required 1000 Hz.

In this way it is possible to  select any frequency  in the audio band and at the same time continuously vary the addition or subtraction level of these frequencies to whatever is required. Remember, the attenuation can still be increased or decreased at the same time as changing the center frequency (!), which allows unlimited control of the frequency addition and subtraction over the entire audio reproduction range!

Fig. 7 shows again the attenuation centered on 1 kHz but this time with less attenuation than in Fig. 6, both controls having been moved to somewhat less subtraction the 800 Hz and 3.2 kHz.

Fig. 8 displays the attenuation curve when two of the controls, in this case 200 Hz and 800 Hz, are set to full subtraction and the non-symmetrical switch is pushed in. This way one is able to achieve very pronounced attenuation.

Note that as both controls are set to the same level of subtraction the center frequency is at exactly the harmonic middle between the two controls (200 Hz and 800 Hz), in this case 400 Hz showing the musically correct function of the Linearizers.

Fig. 9 If, for instance, certain sharper resonances in a recording (e.g. horn resonances of early record-ings) have to be subtracted from the original signal, a good example is displayed in  Fig. 9.Here the subtraction control is set to -6 at 800 Hz and -3.5 at both 200 Hz and 3.2 kHz. A resonance that - in this case - would be centered at 800 Hz could be subtracted from the direct signal with a quite profound attenuation of - in this case - 32 dB! Of course this is an extreme value and almost never required in actual use.

These figures only show a few of the myriad possibilities. The combination of just five dynamic controls allows a literally  unlimited number of musically relevant linearization / correction curves to be created.