BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an audio processing apparatus in accordance with a preferred embodiment of the present invention;
FIG. 2 shows a first embodiment of details of function units of the audio processing apparatus of FIG. 1; and
FIG. 3 shows a second embodiment of details of function units of the audio processing apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to FIG. 1, the audio processing apparatus 20 in the preferred embodiment is an acoustic equipment 20 connected between an audio source 10 and audio output 30 such as a speaker. The acoustic equipment 20 is configured with a mode select switch 250. The mode select switch 250 is operable to change the acoustic equipment 20 between a normal mode and a karaoke mode. In the normal mode audio signals from the audio source 10 is amplified by an amplifier 240 in the acoustic equipment 20 and then transmitted to the audio output 30.
In the karaoke mode the audio signals is filtered to remove vocal signals by a vocal removing unit 210, changed a pitch by a pitch change unit 220, amplified by the amplifier 240 and then transmitted to the audio output 30. A mode selector 230 is employed to change the mode of the acoustic equipment 20 according to the mode select switch 250. In the preferred embodiment the mode selector 230 is a changeover switch 230 that either connects the audio source 10 to the amplifier 240 or the pitch change unit 220 to the amplifier 240.
In alternative embodiments, the changeover switch 230 connects the audio source 10 either to the vocal removing unit 210 or to the amplifier 240. The amplifier 240 is controlled by a volume adjust switch 260 configured on the acoustic equipment 20. The volume adjust switch 260 is operable to obtain a suitable output volume from the audio output 30.
Referring to FIG. 2, the vocal removing unit 210 mainly includes a high pass filter 211, a low pass filter 212, and a mixer 213. The high pass filter 211 and the low pass filter 212 are connected in parallel between the audio source 10 and the mixer 213. The high pass filter 211 and the low pass filter 211 cooperatively filter out middle frequency components that are considered to include vocal signals from the audio signals. In depth, the high pass filter 211 passes high frequency components and the low pass filter 211 passes low frequency components from the audio signals to the mixer 213. The mixer 213 mixes the high frequency components with the low frequency components to produce mixed audio signals and output the mixed audio signals to the pitch change unit 220. Generally, the high pass filter 211 and the low pass filter 212 have suitable cutoff frequencies to efficiently remove the vocals from the audio signals. In alternative embodiments, a bandstop filter may be employed to constitute the vocal removing unit 210. The bandstop filter also has suitable cutoff frequencies to efficiently remove the vocals from the original audio signals.
The pitch change unit 220 includes an A/D (analog to digital) converter 221, and a D/A (digital to analog) converter 223 connected in series with the A/D converter 221. A clock circuit 222 is employed to provide clock signals both to the A/D converter 221 and the D/A converter 223. The A/D converter 221 has a sampling rate different from that of the D/A converter 223 in order to change the pitch of the mixed audio signals when the mixed audio signals are put through the pitch change unit 220. For example, if the D/A converter 223 has a sampling rate (hereinafter refers to as “D/A sampling rate”) higher than that of the A/D converter (hereinafter refers to as “A/D sampling rate”), the pitch of the mixed audio signals is raised by the pitch change unit 220. Otherwise, if the D/A sampling rate is lower than the A/D sampling rate, the pitch of the mixed audio signals is lowered by the pitch change unit 230. The pitch of the mixed audio signals is either lowered by a factor of N (N is a natural number ranging from 1 to 7) degrees if the D/A sampling rate is (1−N/16) times than the A/D sampling rate, or raised by a factor of N degrees if the D/A sampling rate is (1+N/8) times than the A/D sampling rate.
In alternative embodiments the pitch change unit 220 may include more than one D/A converters. FIG. 3 depicts an alternative embodiment of the pitch change unit 220 that includes two D/A converters. The two D/A converters refer to as a first D/A converter 224 and a second D/A converter 225 that both receive the clock signals from the clock circuit 222. The first D/A converter 224 has a sampling rate different from that of the second D/A converter 22. The first D/A converter 224 and the second D/A converter 225 are both connected to the A/D converter 221 via a pitch select circuit 226. The pitch select circuit 226 in this embodiment is also a changeover switch 226 that connects either the first D/A converter 224 or the second D/A converter 225 to the A/D converter 221 by a pitch select switch 270 configured on the acoustic equipment 20. The pitch select switch 270 is operable to select a suitable output pitch from the audio output 30.
In the embodiment relative to FIG. 3, there are two pitch selections. However in embodiments when more than two D/A converters are employed, there may be more than two pitch selections. In those embodiments, the D/A converters are connected to the A/D converter 221 via the pitch select circuit 226 which may be a multiplex switch.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
Patent Application
20080075292
