GB2265286A - Audio mixing circuit - Google Patents

Abstract

An audio mixing circuit 10 with a number of input channels 11 to 15 comprises a splitter control circuit 40 for repeatedly interrupting an audio signal. Separate controls (44, 46, Fig. 2 not shown) are provided for setting the durations of each interruption and the time between interruptions. An echo circuit 30, connected to the splitter control circuit 40, permits repeated playing of a short part of an audio signal. Kill switches 60, 62 separate out one or more frequency bands from selected ones of the input channels 11 to 15. <IMAGE>

Description

Audio Mixing Circuit The present invention relates to a pre-amp audio mixer.

Audio mixers are used for many different purposes, all based around mixing different sounds together, whether they are different records, instruments or microphones, etc. The present invention relates to the type of mixer used by disc jockeys for mixing records, CD's, tapes, tuners and DAT's one to another. Such mixers usually comprise a number of different channels which are mixed down to one or two outputs (depending on mono or stereo) passing through a selection of features.

The present invention seeks to provide an audio mixing circuit with an improved range of signal handling possibilities for a user.

According to a first aspect of the present invention, there is provided an audio mixer circuit with a splitter control circuit for repeatedly interrupting an audio signal, the splitter control circuit comprising means for setting the duration of each interruption and means for setting the duration for which the audio signal passes between successive interruptions.

According to a second aspect of the present invention, there is provided an audio mixer circuit with a separation control circuit connected at the output thereof, said separation control circuit acting to balance the output signals of the mixer circuit.

According to a third aspect of the present invention, there is provided an audio mixer circuit with a plurality of audio input channels and at least first and second sets of kill switches for separating out one or more selected ranges of frequencies from audio input signals, said first set of kill switches being arranged to receive signals from one or more of said input channels and said second set of kill switches being arranged to receive signals from one or more of the remaining input channels.

According to a fourth aspect of the present invention there is provided an audio mixer circuit with a plurality of audio input channels and at least first and second graphic equalisers, said first graphic equaliser being arranged to receive signals from some of said input channels and said second graphic equaliser being arranged to receive signals from at least some of the remaining input channels.

A preferred embodiment of the present invention incorporates features in accordance with all four of the above aspects of the present invention. Alternative embodiments comprise combinations of any two or three of the above aspects.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures, of which: Fig. 1 shows a block schematic diagram of an audio mixing circuit and an associated pair of headphones; and Fig. 2 is a front view of the control panel of the audio mixing circuit.

Referring to the drawings an audio mixer 10 has five input channels 11 to 15 each with a respective gain control circuit. Channels 11 to 14 have the option to switch between "phono" and "line" inputs, "phono" being a record player, and "line" being any other input such as tape, tuner, CD, or DAT.

The other channel 15 is a microphone input. This is suitable for most microphones. It also has an adjustable tone control circuit 16, a gain control 18 and a three position voice over switch 19. Switch 19 has the following three positions, viz: a first "on" position, an "off" position, and a second "on" position in which the music is cut out by about 12dB.

The mixer also comprises an electronically simulated echo chamber 30 and a splitter circuit 40. The echo chamber is an analogue unit which takes a portion of the original signal, passes it through a low pass filter, which delays it for a short period. It is then passed through another low pass filter and this is then superimposed on the original signals, also feeding the delayed signal back into the delay IC, so giving it an echo effect. The echo chamber 30 has three control variables, viz: balance, repeat and delay. Balance is the percentage of the delayed signal which is superimposed on the original signal. "Repeat" is the percentage of the delayed signal which is fed back into the delay system. "Delay" is the period by which the signal is actually delayed by the IC.

These three variables are adjusted by respective knobs 32, 34, 36 on the control panel.

Splitter circuit 40 cuts out the music for a very short period controllable by a "mark" variable. It then allows the music to play for a very short period controllable by a "space" variable. This continues repeatedly for as long as the "splitter" function switch 42 is held down.

This is a momentary switch, not a latching one. The mark and space variables are adjusted by respective knobs 44, 46 on the control panel.

The splitter circuit 40 produces a staggered signal which can be used by the user for many different purposes, i.e.

when "scratching" to enhance the effect, or when mixing from one record to another. "Scratching" is an effect often practised by disc jockeys and involves moving a record backwards and forwards repeatedly in contact with a stylus; it thus involves the repeated playing of a short part of the audio signal.

The splitter circuit is placed before the echo chamber 30 allowing, if required, both circuits to work in conjunction with each other. The "splitter" and "echo" functions can work with any one of the five channels by assigning the required channel with the selector control, which comprises a set of five interlocking switches 2125.

A cross fader 50 is also provided which allows the disc jockey to fade between channel 11 and channel 12, allowing either or both channels to play together (control centre) or to slowly fade out one channel when the control is moved to the opposite side.

The mixer 10 further comprises so-called "kill" switches 60, 62, graphic equalisers 70, 72 and separation control circuits 80, 82 which each act like a balancer. Each kill switch is a three way unit which separates the bass, midrange and treble frequencies with filters which allows the user to cut out each one separately leaving the remaining frequencies intact.

e.g. BASS CUT: leaving mid and treble BASS & MID CUT : leaving treble MID & TREBLE CUT: leaving bass This gives absolute control. When mixing, channels 11 and 13 use the left set of switches 60 and channel 12 and 14 use the right set of switches 62.

Each graphic equaliser increases or decreases the amplitude of the various preset frequencies to redefine the clarity. In conventional circuits these are set up as one graphic equaliser for the overall output or two graphic equalisers, one for each individual channel (i.e. left and right outputs). In the present embodiment the two graphic equalisers are set up to work with the input signals, e.g. channels 11 and 13 both use the left equaliser 70 and channels 12 and 14 both use the right equaliser 72, allowing the user to change the characteristics of each particular song individually, and not each individual speaker. The equaliser stage has a by-pass function switch 74 allowing the user the option of the equalisation being on or off.

The separation control circuits 80, 82 are each similar to a balance control circuit. They allow the balance of the output channels to change with regard to the input channels. For example, the balance can be adjusted of channel 11 or channel 13 with the left separation control circuit 80, while the balance of channel 12 and channel 14 can be adjusted with the right separation control circuit 82.

This separation control can work in conjunction with other features, e.g. channel 11 can come out of the left speaker only, while also cutting out bass and treble with the "kill switches". This leaves the vocal frequency in the left speaker while channel 12 can then be played out of both speakers and channel 11 can then be faded between both output channels. As this mixer is mono, but has two output channels this is possible.

The outputs of circuits 80, 82 are fed to respective mixer outputs O/P (and thence to a power amplifier and a loudspeaker) and to respective visual display units, such as voltmeter-type needle indicator devices.

A set of headphones 90 may be also provided, having a cross-fader 98. With these the user can listen to any channel before the signal is changed in any way by the effects. This is controlled by two sets 92, 94 of four interlocking switches by assigning or selecting one channel from each block 92, 94. One can then fade between the two chosen channels. (The term "channels" in this case also embraces a mixed output). The headphones also have an adjustable volume control 96.

An advantage of the above mixer is that it enables distinctive effects to be quickly and easily achieved by a user. The relationship between the vocals and the music for example can be changed at will.

Claims (9)

1. An audio mixer circuit with a splitter control circuit for repeatedly interrupting an audio signal, the splitter circuit comprising means for setting the duration of each interruption and means for setting the duration for which the audio signal passes between successive interruptions.

2. A circuit according to claim 1, wherein the splitter control circuit is controlled by means of a momentary switch.

3. A circuit according to claim 1 or 2, wherein the splitter control circuit comprises means for setting the duration of each interruption and separate means for setting the duration between successive interruptions.

4. A circuit according to any preceding claim, wherein the splitter control circuit is connected to an echo circuit having respective control means for balance, repeat and delay.

5. A circuit according to any preceding claim comprising a plurality of input channels which are selectively connected to the splitter control circuit by a set of interlocking switches.

6. A circuit according to any preceding claim with a plurality of audio input channels and at least first and second sets of kill switches for separating out one or more selected ranges of frequencies from audio input signals, said first set of kill switches being arranged to receive signals from one or more of said input channels and said second set of kill switches being arranged to receive signals from one or more of the remaining input channels.

7. A circuit according to any preceding claim with a plurality of audio input channels and at least first and second graphic equalisers, said first graphic equaliser being arranged to receive signals from some of said input channels and said second graphic equaliser being arranged to receive signals from at least some of the remaining input channels.

8. An audio mixer circuit with a plurality of audio input channels and at least first and second sets of kill switches for separating out one or more selected ranges of frequencies from audio input signals, said first set of kill switches being arranged to receive signals from one or more of said input channels and said second set of kill switches being arranged to receive signals from one or more of the remaining input channels.

9. An audio mixer circuit substantially as herein described with reference to the accompanying drawings.