Electrical audio signal processing systems and devices – Including frequency control – Having automatic equalizer circuit
Patent
1994-05-09
1998-04-28
Kuntz, Curtis
Electrical audio signal processing systems and devices
Including frequency control
Having automatic equalizer circuit
381106, H03G 500
Patent
active
057455856
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an equalization method and device for audio frequency amplifiers for reproducing sound.
In the reproduction of sound, equalization is directed to obtaining either a sound balance as close as possible to the original sound by correcting defects in the linearity of the response curve of the transducer system comprising one or more loudspeakers, representing the concept of high fidelity, or a sound tailored to the taste of the listener. In the former case the function of the equalization device or equalizer is purely technical. In the latter case the equalizer serves as a sophisticated tone control.
The response curve of a loudspeaker enclosure in a room is subject to two kinds of distortion: very peaky "sawteeth" and broader undulations. At the lower end of the audible frequency spectrum these two types of distortion are combined.
The sawtooth distortion results from interaction between the direct sound wave and reflected sound waves. If the direct wave and the resultant of the reflected waves are in phase the response curve shows a peak of approximately 6 dB relative to the anechoic pressure due to the direct wave only. If the resultant of the reflected waves is 180.degree. out of phase with the direct wave the response curve shows a dip and in theory the acoustical pressure can cancel out.
The broader undulations are due to the non-linearity of the response curve of the enclosure at the listening angle.
With known equalization devices, equalization is obtained by including permanently in the signal path bandpass filters adapted to fill in the dips of the response curve and bandstop filters adapted to remove the peaks.
This procedure gives good results for correction of undulations resulting from non-linearity of the response curve of the enclosure, but has an adverse effect when applied to the correction of peaky distortion resulting from a combination of the direct wave and the reflected waves in a room.
During investigation of transient phenomena, the applicant has discovered that the combination of the direct wave with the reflected waves occurs progressively and stabilizes only after a time period which can be up to 100 ms in an ordinary size room, for example a 100 m.sup.3 living room. This effect can be called the "room effect".
A signal peak due to the audible attack of a musical instrument is always reached within the first 10 milliseconds, at which time the room effect has yet to occur. This means that only the direct wave has reached the listener.
Given that conventional equalizers process only stable phenomena, with no effect on reproduction of transient phenomena, instrumental attack whose fundamental frequency corresponds to a resonance peak that is corrected by a conventional equalizer causes the dynamic range of the signal to be cut by around 6 dB, a power ratio of 1 to 4. The same applies on correcting a dip by adjusting a frequency band using a conventional equalizer, which artificially increases the dynamic range in this frequency band.
An object of the invention is to propose an equalization method and device allowing for transient phenomena.
To be more precise, an object of the invention is an equalization method and device allowing for the room effect and preserving the original dynamic range of instrumental attack.
The present invention features an equalization method for amplification of audio frequency signals characterized in that it provides first means for correcting the response curve under stable conditions and at least one second correction means whose gain (GT) is different from the gain (GS) of the first correction means for correcting the response curve under transient conditions, discriminates transients, switches from the first correction means to the second correction means when a transient is discriminated and switches in the opposite direction after the transient.
The discrimination of the transient and the switching from the first correction means to the second correction means are preferably effected within less than 5 ms in order to re
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Kuntz Curtis
Mei Xu
S L X S.A.R.L.
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