U.S. Philips Corporation

Jacob M Van Nieuwland

Franciscus J Op De Beek

Joris A Nieuwendijk

Georgius B Sanders

Wilhelmus D Van Gijsel

Johannes Leopoldus Bakx

Johan M Rijnsburger

Johannes W Kemna

Jan J Janse

Heemskerk: Jacobus P J

The invention relates to a magneto-optical recorder with magnetic-field modulation. It comprises a laser (8) for producing a light beam (6), an optical focussing system (9) for forming a focal spot (12), and a servo device (10) for maintaining the focal spot (12) in focus on the surface of a thermo-magnetic record carrier (4), and for supplying a correction signal (V.sub.c) which is representative of the position of the surface of said carrier. A current modulator modulates the current through a coil (15) of a magnetic head. A compensation device (7) is responsive to said correction signal (V.sub.c) to change a parameter influencing the field of the coil, in such a way that the field strength at the surface of said carrier (4) is substantially independant of the position of said surface.

Magneto-optical recorder with servo control system for a magnetic-field

A manually operated or automatic equalizer (1) with adjustable band filters for varying the frequency characteristic of an electric signal presented to an input (2) and for applying a frequency characteristic-adapted electric signal to an output (3). The equalizer has a plurality of band filters (F.sub.1 to Fn) with their bands located adjacent to one another in a given frequency range. The distance (frequency separation) between the central frequencies of filters having neighboring bands is greater than the distance between the central frequencies of one third octave filters having neighboring bands located at at least approximately the same frequencies as those of the band filters (F.sub.i). At least those band filters (F.sub.1 to F.sub.m) whose bands are located in the low-frequency part (f&lt;450 Hz) of the frequency range have a central frequency (fc.sub.i) which is variable. A digital filter which can be used as a band filter in the equalizer is also described.

Equalizer with adjustable band filters and a digital filter suitable for

The equalizing arrangement in accordance with the invention comprises an equalizing unit (4) for correcting the frequency characteristic of an electric signal applied to its first input (7) under the influence of a control signal (10) applied to its second input (8) and for supplying a corrected electric signal to its output (9), and a frequency analyzing unit (16) having a first input (15) coupled to a point in the signal path between the input terminal (1) and the first input (7) of the equalizing unit (4), a second input (17) coupled to the pick-up means (14) and an output (19) for supplying the control signal (10). The analyzing unit (16) is constructed to apply a Fourier transform to the previously digitized input signals x(t) and y(t) applied to its first and its second input, to compute Fourier-transformed signals F.sub.x (f) and F.sub.y (f) of these two signals and to compute a transfer function between these two signals. Preferably the frequency analyzing unit is further constructed to compute a coherence function .gamma..sup.2.sub.xy (f) between the two signals and, in determining the control signal, to ignore the values of the transfer function for those frequencies f.sub.i for which .gamma..sup.2.sub.xy is smaller than a specific value, for example 0.8. By means of the arrangement in accordance with the invention a better equalization can be achived and the distortion of the output signal of the arrangement is low.

Automatic equalizing system with DFT and FFT

A loudspeaker system for converting an n-bit digitized electric signal (11) into an acoustic signal comprises an electrodynamic loudspeaker (1) with n voice-coil sections (4.1, 4.2, . . . 4.n) which cooperate with a magnet system (3). The loudspeaker system further comprises means (18.1, 18.2, . . . 18.n) for short-circuiting a voice-coil section if the value of the bit corresponding to the voice-coil section is such that the relevant voice-coil section is not driven.

Loudspeaker system and loudspeaker for use in a loud-speaker system for

In a loudspeaker system for converting an n-bit digitized electric signal (6) into an acoustic signal a plurality of sections (voice coils 14.1, 14.2, 14.3, 14.p) of a digital loudspeaker (1) are driven directly by the p most significant bits of the n-bit digitized electric signal (6). The loudspeaker (1) comprises at least one additional section (14.p+1). This (p+1).sup.th voice coil receives a signal from a digital-to-analog converter (5), the input signal of the digital-to-analog converter comprising at least the n-p least significant bits (FIG. 2). In a different embodiment the digital-to-analog converter (5) receives all the n bits of the digitized electric signal as the input signal. At least the p sections (14.1 to 14.p) which correspond to the p most significant bits are provided with means (the resistances r) for producing a signal which is a measure of the sum of their instantaneous drive signals and for applying the said signal to a signal combination unit (32) arranged in the line (10) from the output of the digital-to-analog converter (5) to the (p+1).sup.th section (R.sub.1). By means of this correction circuit the distortion in the loudspeaker system can be reduced substantially (FIG. 3b).

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Eindhoven, Netherlands

Jacob M Van Nieuwland