Monday, April 22, 2013

FM Acoustics 268-C Linearizer - How it works part 1

The FM 268-C features a built in Harmonic Linearizer that allows adjusting the strength (or weakness) of critical frequencies. Thanks to this absolutely unique solution which only uses five easy to adjust controls, any frequency (or group of frequencies) in the entire audio band can be optimized and this without negative influence on the audio signal. The FM 268-C does what musicians, engineers and music enthusiasts the world over have been dreaming about for dozens of years.

For the first time, obnoxious sounds from any source can be attenuated (subtracted) and weaknesses of certain parts of the music spectrum can be strengthened. All this is done whilst the characteristics and transparency of the original signal are kept pristine and while remaining purely in the analogue domain.

The improvements are described anyway from "amazing" to "quite incredible".

The unique concept guarantees that all of the above is done without any negative influence on the signal path. In fact, the method of operation is rather intriguing as can be seen from Fig. C: the entire audio signal is directed right through from input to output avoiding phase changes and all other negative influence. The actual response improvement is done by a unique additive/subtractive phase accurate bank of 5 individual Linearizers that combined can correct any frequency aberration in the audio band. The signal always passes  straight through from the input to the output even when the strength of a band is adjusted via the front panel controls.

While looking at the control panel of the FM 268-C linearizer section one could be reminded of an equalizer. However, the FM 268-C Harmonic Linearizer's mode of operation is rather different and avoids all the problems of equalizers. It's singular characteristics allow linearization of any source by only adding or subtracting critical areas of the audio signal to/from the direct through signal.
The result: in the FM 268-C there is no ripple in the pass band and no phase shift / discontinuity, which results in pristine signal coherence and superb transient response.
A further unique characteristic is that when all level controls are in full boost position there is no change in frequency response; a linear gain over the entire frequency range is achieved; this is unique, the sign of perfect linearization.

The following figures and explanation help to better understand the results of this unique development that revolutionizes the way music is reproduced.

To appreciate the massive difference between the FM 268-C Harmonic Linearizer and filter/equalizers circuits some explanation is helpful. Fig. A shows a block schematic of a typical equalizer/filter and Fig. B shows a more detailed schematic of such a unit. One can see how the linear signal is tampered with, introducing all kinds of negative effects to the signal while trying to correct some arbitrarily chosen frequency bands that are not necessarily music related. In Fig. A and Fig. B the filter circuits containing resistors/capacitors/coils or - even worse - active reactance are connected in the feedback loop. By changing them the feedback configuration of the circuit is changed also! This is a poor solution because if feedback is used, it must be linear and identical for all frequencies. With frequency dependent feedback - as in such circuits - some of the music range will have higher distortion, inter-modulation and other
negative effects than other parts of the music range.

Furthermore, one can easily see that such an equalizer configuration creates massive phase errors.

In contrast, Fig. C shows the block schematic of the FM 268-C linearizer section.

The input signal enters FM ACOUSTICS exclusive discrete Class A linear amplifier stage from which the signal goes 100% direct-through to a discrete Class A linear output amplifier. At the same time the input signal is routed to individual linearizer controls and then enters a bank of constant phase additive/subtractive Linearizers. These have the unique capability of either subtracting from or adding to the direct through signal without creating any negative influence. This unique system allows very fine corrections to be made without the usual drastic phase changes, frequency dependent feedback distortion and other negative influences on the audio signal.

The result: massive improvements in reproduction without any negative influence on the audio signal.

The FM 268-C Harmonic Linearizer has been designed with optimal reproduction of musically relevant information in mind. Therefore, boost and cut levels are kept to an optimal but not excessive range.

To achieve this ultra-accurate selection extremely tight component tolerances are required. No op-amps, IC's, transformers or hybrid circuits can be used. In the tradition of FM ACOUSTICS discrete enhanced Class A precision buffers are employed to assure that no loading, phase changes, non linearity or other negative effect can occur.