Method and device for extension of low frequency output from a loudspeaker
View Patent ↗A method and device for enhancing low frequency content of an input signal (X), e.g. bass boosting of an audio signal. An overdriving (ODR) of a low frequency signal part (LS 1 ) of the input signal (X) is performed to produce a boosted low frequency signal (LS 3 ), wherein the overdriving (ODR) includes amplifying the low frequency signal part (LS 1 ) by a first gain (G 1 ) to form an amplified low frequency signal (LS 2 ), and hard-clipping (CLP) the amplified low frequency signal (LS 2 ) to form the boosted low frequency signal (LS 3 ). A first low-pass filtering (LPF 1 ) is then performed, resulting in a processed low frequency signal (LS 4 ). A cut-off frequency of the first low-pass filtering (LPF 1 ) is selected so as to reduce distortion components introduced by the overdriving (ODR). Finally, the processed low frequency signal (LS 4 ) is combined with at least part of the input signal (X) to form an output signal (Y). Preferred embodiments further include adding a part of the input signal (X) after a gain (G 2 ), to the low frequency signal part (LS 1 ), hereby taking into account possible high frequency peak in the overdriving (ODR) process. Preferably, a second low-pass filter (LPF 2 ) serves to low-pass filter the input signal (X) to form the low frequency signal part (LS 1 ). A second cut-off frequency of the second low-pass filter (LPF 2 ) is preferably selected coincident with the first cut-off frequency. Further, the first and second cut-off frequencies are preferably selected equal to, or within one octave from, a low frequency cut-off frequency for a loudspeaker intended to reproduce the output signal (Y). Thus, the preferred method introduces a level dependent bass boost below the loudspeaker s low frequency cut-off frequency.
1. A method of enhancing low frequency content of an input signal, comprising:
a) performing a first low-pass filtering of the input signal to provide a low frequency signal part, and combining a portion of the input signal with the low frequency signal part prior to performing an overdriving of a low frequency signal part of the input signal to form a boosted low frequency signal in order to take into account possible high frequency peaks, leading to a lower boost of the low frequency signal, thereby reducing the risk of clipping distortion in the output signal, wherein the overdriving comprises amplifying the low frequency signal part of the input signal by a first gain to form an amplified low frequency signal, and hard-clipping the amplified low frequency signal to form the boosted low frequency signal,
b) performing a second low-pass filtering of the boosted low frequency signal to form a processed low frequency signal, wherein a first cut-off frequency of the second low-pass filtering is selected to reduce distortion components introduced by the overdriving, and
c) combining the processed low frequency signal with at least part of the input signal to form an output signal.
2. The method according to claim 1 , wherein a second cut-off frequency of the second low-pass filtering is substantially equal to the first cut-off frequency of the first low-pass filtering.
3. The method according to claim 1 , wherein the first cut-off frequency is selected such that it is within one octave around a low frequency cut-off frequency of an associated electro-acoustic transducer intended to convert the output signal to an acoustic signal.
4. The method according to claim 1 , wherein the first gain is in the range +3 dB to +30 dB, such as in the range +6 dB to +20 dB.
5. The method according to claim 1 , wherein a second gain is applied to the input signal before being combined with the low frequency signal part, wherein the second gain is in the range −20 dB to 0 dB.
6. The method according to claim 5 , wherein the second gain applied to the input signal before being combined with the low frequency signal part is in the range −10 dB to −3 dB.
7. The method according to claim 1 , further comprising performing a high-pass filtering of the input signal to form a high frequency signal part prior to combining with the low frequency signal part.
8. The method according to claim 7 , wherein step c) includes combining the high frequency signal part with the processed low frequency signal to form the output signal.
9. The method according to claim 1 , further comprising applying a third gain of less than zero dB after step a).
10. The method according to claim 1 , further comprising performing a signal clipping after the combining in step c).
11. A signal processor arranged to perform the method according to claim 1 .
12. A device that comprises the signal processor according to claim 11 .
13. The device according to claim 12 , wherein the device is an audio device, a communication device, a car audio device, a home audio device, a headphone, a personal computer, a TV set, a personal media player, a gaming console, a hearing aid, or a hi-fi device.
14. A system comprising the device according to claim 12 , further comprising an electro-acoustic transducer.
15. A non-transitory, computer readable storage medium with a computer executable program code adapted to perform the method according to claim 1 .