Abstract: A digital filter of the present invention is an FIR type digital filter arranged such that an input data converting circuit samples input data at a rate N times as fast as a sampling frequency fs, and outputs the input data for a 1/N period of a sign interval T and “0” for the rest of the period. A changeover switch switches between an output from a take-out tap of actual input data and interpolation data obtained by an adding action of an adder circuit, and outputs the switched data as output data. Hence, even if the input data shape a rectangular wave pulse, a resulting state is equivalent to the one when an impulse train is inputted. Thus, since the impulse response characteristics of a roll-off filter can be utilized, outputs from each pair of taps supplied with the same coefficient are added to each other by an adder, and each addition result is multiplied by their respective coefficients by a multiplier.

Abstract: A blackened steel strip having improved blackness is produced in an efficient manner by anodizing a zinc alloy-plated steel strip in a solution containing 5 to 100 g/l of ClO.sub.3.sup.- and 10 to 300 g/l of SO.sub.4.sup.2- at pH 0.5 to 2.5 at a temperature of 30.degree. to 75.degree. C. and with a quantity of electricity of 10 to 300 C/dm.sup.2, and forming an acrylic resin chromate layer on the anodized steel strip to a thickness of 0.3 to 2.5 .mu.m. The solution may contain 5 to 100 g/l in total of at least one co-additive selected from Cl.sup.-, NO.sub.3.sup.-, H.sub.2 O.sub.2, Ni.sup.2+, Co.sup.2+, Fe.sup.2+, and Mn.sup.2+. The acrylic resin chromate layer contains 2 to 10 parts by weight of in the form of a chromate Cr per 100 parts by weight of acrylic resin.

Abstract: A connector with a plug having a protruding piece and a jack for accepting it can transmit not only electrical signals but also light signals between devices connected thereby. Optical fibers for transmitting light signals therethrough are placed longitudinally inside the protruding piece of the plug and the jack includes not only electrodes for transmitting electrical signals but also a light emitting element to transmit light signals into the plug through the optical fibers or a light receiving element for receiving light signals transmitted through the optical fibers.

Abstract: A tone control circuit for use in audio equipments includes an attenuating high pass filter (typically, a CR filter), an attenuating low pass filter, a boosting high pass filter, a boosting low pass filter and at least an operational amplifier for tone control. The high pass filters extract a treble component from an audio input signal for emphasizing or attenuating treble response, whereas the low pass filter extract a bass component of the audio input signal for emphasizing or attenuating bass response. The mid-range component of the audio input signal prevented from entering the filters by virtue of a bypass circuit interposed between a source of the audio input signal and the operational amplifier.