WO2000057673A1

WO2000057673A1 - Band stop filter

Info

Publication number: WO2000057673A1
Application number: PCT/EP2000/001907
Authority: WO
Inventors: Ronaldus M. Aarts
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 1999-03-24
Filing date: 2000-03-06
Publication date: 2000-09-28
Also published as: JP2002540697A; KR20010043780A; CN1296722A; EP1080607A1

Abstract

Bass audio signals can give an annoyance of neighbors (non-voluntary listener) of the listener (voluntary listener). To overcome this band block filters are known, but by blocking the audio signals in the frequency band the perception for the listener is less good. The invention overcomes this problem by combining enhancing means to obtain the so-called ultra bass, with the blocking filter.

Description

Band stop filter.

The invention relates to an audio system as described in the preamble of claim 1.

The invention further relates to bass stop filter means.

From the European Patent Application EP-A-0546619 (Applicant's reference PHA 40.624) an audio system is known wherein the bass signal is improved. This is done by using the psycho-acoustic phenomenon often referred to as virtual pitch or missing fundamental, which evokes the illusion of a higher bass response whereon the loudspeaker does not radiate more power at these low frequencies. This illusion can be created by replacing all frequency tones, which are present in the audio signal but cannot be produced by a small loudspeaker, by harmonics of these tones. The harmonics now represent the low frequency tones, the so-called ultra-bass. In this way, the audio signal as received by a listener is improved. In cases where it is not wanted that the low frequency (bass) signals are supplied to loudspeakers, the known audio systems do not perform very well. An object of the invention is to improve the received audio signals in cases where the low frequency signals may not be supplied to the loudspeakers.

To this end a first aspect of the invention provides an audio system as defined in claim 1.

The invention is based on the recognition that in cases where the really low frequency signals are not allowed to be supplied to the loudspeakers, for example, because people living in the neighborhood (the non-voluntary listeners) do not want to hear those bass signals it is possible to block these really low frequency signals and at the same time by using the ultra bass feature to give the people who are listening (the voluntary listeners) to the audio signals the perception that the bass signals are good. An embodiment of an audio signal according to the invention comprises the features of claim 2.

By blocking the low frequency part in the range from 50 till 120 Hz the annoyance of the neighbors (non- voluntary listeners) is reduced to a minimum.

The invention and additional features, which may generally be used to implement the invention to advantage, will be apparent from and elucidated with reference to the examples described below hereinafter and shown in the figure: The figure shows a block schematic example of an audio system of the invention.

The figure shows a schematic example of an audio system AS. At an input I the audio system receives an audio signal. This audio signal is supplied to enhancing means EM. In this example the enhancing means comprise band pass filter means BPF for selecting a part of the audio signal (the low frequency part). The output of the band pass filter means is coupled with a so-called non-linear device (for example a harmonic generator or integrator etc). The non-linear device creates harmonics of the signals, which are supplied by the band pass filter.

The output of the non-linear device is supplied to a low pass filter for filtering out the higher frequency components. The output signal of the enhancing means is supplied to summing means SUM. At the other input the summing means receives a signal from band stop filter means BSF which band stop filter means filter out the low frequency components of the input audio signal for example. The output of the summing means SUM is supplied to the output O of the audio system. The output O can be coupled to loudspeaker means, etc.

The enhancing means EM can for example be implemented as described in EP Application No. 98202998.5 (Applicants reference PHN17'.092), which document and its corresponding applications is herewith incorporated by reference. By creating harmonics of the original audio signal the perception of the low frequency band (the so-called ultra bass) is improved, without the annoyance for non-voluntary listeners (for example neighbors).

One of the differences with the normal "ultra bass" is that in that case either the loudspeakers or the transmission channel is limited in the lower frequency band. In the situation of the invention concerned there is no limitation in neither the transmission channel (or in the audio player) nor in the loudspeakers but the limitation here is the annoyance of the neighbors.

With this audio system it is possible to, at one end, overcome the nuisance the neighbors (non- voluntary listeners) of the listener (voluntary listener) can have from low frequency signals (bass signals). This is achieved by the bass stop filter means BSF. And at the other hand to improve the perception of the audio signal by the listener with the enhancing means.

Claims

CLAIMS:

1. Audio system comprising an input for receiving an audio signal and an output for supplying an output signal, processing means for processing the received audio signal and enhancing means, the enhancing means comprising selecting means for selecting a part of the audio signal, a signal generator for generating a signal in dependence of the selected part of the audio signal and summing means for summing the audio signal with the enhanced part of the audio signal, characterized in that the audio signal comprises band stop filter means between the input and the summing means for stopping a part of the audio signal.

2. Audio system according to claim 1, characterized in that the band stop filter means have a frequency band from 50 till 120 Hz.

3. Blocking filter means for use in an audio system according to claim 1 or 2.