GB2044484A - Visual display apparatus - Google Patents

Abstract

A visual display of varying colour and/or intensity is produced by a display apparatus in response to one or more audio frequency inputs (10). Each audio input is pre-amplified and passed through a logarithmic amplifier (12) and a number of filter channels (14, 15, 16) to provide analogue outputs which may be used to control switching of individual lamps (19) or to control variation of other visual display devices. <IMAGE>

Description

SPECIFICATION Visual display apparatus This invention relates to apparatus for the production of visual displays in response to audio input signals.

An object of the invention is to provide visual displays of varying colour and/or intensity which respond automatically to audio inputs derived, for example, from a tape recording, record player, public address system or microphone.

According to the invention there is provided an apparatus for producing visual display of varying colour and/or intensity in response to at least one audio frequency input signal, comprising a logarithmic amplifier for the or each audio signal, a number of filter channels connected to the output of the logarithmic amplifier and tuned to different frequency ranges, and output circuit means connected to the filter channels for providing analogue output signals for control of visual display means.

In a preferred embodiment of the invention the apparatus would have a number of audio inputs in different frequency ranges, and associated filter channels tuned to the different frequency ranges so as to produce a visual display in which the displayed light intensities, for example of different colours, are controlled independently in response to the different respective audio inputs, thereby in effect converting sound, for example, musical sound, into a corresponding light display, for example a varying colour display.

The use of a logarithmic amplifier in the present invention for the purpose of converting the audio signals into the visual display output signals is advantageous, since the response of the human ear to changes in sound intensity is logarithmic, while the response of the human eye to changes in light intensity is approximately linear. In effect the filter channels produce a number of analogue output signals which represent different frequency components of an audio input signal.

Preferably a sweep signal generator is connected to the logarithmic amplifier to sweep the frequency of the signals supplied to the filter channels.

The sweep signal generator maintains a continuous variation in the output of the apparatus in the absence of an audio input signal.

The output circuit means may comprise electronic switching elements the firing angles of which are determined by the outputs of the filter channels. Thus in a preferred embodiment each filter channel comprises a Wien bridge oscillator tuned to a predetermined frequency band and an associated rectifier arranged to provide a direct-current output proportional in amplitude to the amplitude of the input signal in said frequency band.

A ramp signal generator may be provided to generate a ramp signal which is compared with the direct-current outputs derived from the filter channels to generate pulses the phase of which is dependent upon the amplitude of said filter outputs.

The invention will be further described, by way of example, with reference to the accompanying purely diagrammatic drawing which is a schematic diagram of an apparatus according to one embodiment of the invention.

The illustrated apparatus according to the invention is designed to receive audio input signals through several input channels 10, shown diagrammatically in Fig. 1, and derived from, for example, a microphone or microphones, a tape play-back head or a record pick-up. The input signals are summed and amplified in a pre-amplifier stage 11, the amplified output of which is passed to a logarithmic amplifier 1 2 and to an auto-sweep generator 1 3.

The auto-sweep generator 1 3 comprises a variable frequency oscillator the frequency of which is swept cyclically through the audio frequency range. The output of the autosweep generator 1 3 is connected through a selector switch to the logarithmic amplifier 1 2 to provide an input to the latter in the absence of any audio inputs on the input channels 10, the sweep generator output sweeping in frequency continuously and cyclically so as to ensure a dynamic output from the apparatus in the absence of any audio intput.

The output of the pre-amplifier 11 is amplified logarithmically by the logarithmic amplifier 12, the output of which passes to a number of filter channels. In the illustrated embodiment there are fortysix different bandpass filters 14 tuned to different frequency ranges. In addition, the logarithmic amplifier output is passed through a low-pass filter 1 5 which accepts frequencies below 65 Hz and a high-pass filter 1 6 which accepts frequencies above 2 KHz.

The outputs of the filters 14, 1 5 and 1 6 comprise respective signals the amplitudes of which represent, on a logarithmic scale, the relative amplitudes of the audio input components in the different frequency ranges of the filter channels. These are, in effect, analogue output signals which can be used to produce variations in intensity of visual displays of different colours.

For example, the visual displays may be provided by a number of television picture tubes, in which case the analogue output signals from the filters 14, 1 5 and 1 6 may be employed directly to effect variation in the displayed brightness and/or colour of the picture tubes. Alternatively, the analogue output signals from the filters may be employed to vary the intensity of respective light sources or display devices. In the illustrated apparatus the visual display is formed by a series of lamps; in which case a power switching circuit 17 is employed, as shown, to effect selective switching of a mains power supply 18 to individual lamps 1 9 connected to respective output ports 20 of the switching circuit.

The lamps 19, which may be of different colours, may form a lighting array for illuminating, for example, a wall or ceiling surface, or a translucent panel.

The apparatus can be arranged to provide a visual display of changing colour and/or intensity pattern by the selective switching of the lamps 19, correlated to variations in the frequency of audio input signals applied to the input channels 10, when such signals are present, or correlated to the cyclic sweeping of the generator 1 2 in the absence of any audio inputs on the channels 10.

The pre-amplifier 11 has a number of amplifier stages for each audio input channel, the gains of the amplifiers being selected according to the sources of the input signals. The outputs of the amplifier stages are summed and then amplified in a further amplifier stage before passing to an audio transformer which isolates the common connections of the preamplifier for the rest of the system, thereby preventing inteference being fed back to the pre-amplifier from the output stages.

The logarithmic amplifier 12, to which the output of the pre-amplifier 11 is fed, includes a variable gain amplifier stage and further amplifier stages connected to a logarithmic amplifier integrated circuit (for example type TL441) which produces the required logarithmic output signal.

The auto-sweep generator 1 3 monitors the output of the pre-amplifier 11 and detects the absence of any audio signal input on any of the input channels 1 0. Absence of an audio input for a predetermined time interval causes automatic energisation of the auto-sweep generator 1 3 to provide a dynamic input to the logarithmic amplifier 1 2 of continuously varying frequency, sweeping throughout the entire audio range. The auto-sweep generator 1 3 may include, for example, two standard waveform generator integrated circuits one of which provides a variable DC control voltage and the other of which acts as an oscillator the frequency of which is varied continuously by the DC control voltage of the first integrated circuit.A variable frequency oscillator 1 3A, the frequency of which can be varied manually by the operator over a range 30 Hz-4 KHz, affords a facility for manual variation of the output frequency of the auto-sweep generator 13.

Each of the fortysix band pass filters 14 may consist of a Wien bridge oscillator operating in the relaxation mode. When an input signal of the frequency to which any one of the Wien bridge oscillators is tuned is received from the logarithmic amplifier 1 2 the oscillator in question is activated to provide an output signal the amplitude of which is proportional to the input signal. The pass band of each filter 14 is preset by adjustment of the gain of the respective Wien bridge oscillator.

The output from each band pass filter 14 is rectified and amplified and then passed to a respective switching stage in the power switching device 1 7.

Each switching stage of the power switching device 1 7 may include a comparator to one input of which the output of the associated filter 14 is passed, the other input of the comparator receiving a ramp waveform from a ramp generator 21. The ramp generator 21 may be derived from a 50 Hz mains supply, at twice the frequency of the latter, the resulting ramp waveform being compared in the respective comparator with the DC outputs of the respective filter 14. When the ramp voltage in each cycle of the ramp waveform falls below the DC filter output applied to the comparator a pulse is produced, the trailing edge of which is utilised to fire an associated triac switching device. The firing angle of the triac will therefore be representative of the amplitude of the respective DC signal derived from the associated filter. The ramp voltage from the ramp generator 21 may also be applied to respective comparators in the circuits of the low- and high-pass filters 15, 16, which produce signals which are utilised in associated switching stages to drive background lighting sources.

The ramp signal generator 21 may include two Schmitt trigger circuits which each produce a single shot for the positive and negative edges of the 50 Hz mains supply waveform thereto, resulting in a train of pulses at twice the mains frequency. The ramp signal is produced by removing the charge from an integrating circuit at a rate equal to twice the mains frequency. Additionally, a single preset pulse is produced in each cycle at a manually presettable firing angle providing the necessary dimming control for the light sources, indicated diagrammatically by reference numeral 22.

Claims (7)

1. Apparatus for producing varying colour and/or intensity in response to at least one audio frequency signal, comprising a logarithmic amplifier for the or each audio signal, a number of filter channels connected to the output of the logarithmic amplifier and tuned to different frequency ranges, and output circuit means connected to the filter channels for providing analogue output signals for control of visual display means.

2. Apparatus according to claim 1, in which a sweep signal generator is connected to the logarithmic amplifier to sweep the frequency of the signals supplied to the filter channels.

3. Apparatus according to claim 1 or claim 2, in which the or each audio signal is fed to the logarithmic amplifier through a preamplifier stage.

4. Apparatus according to any one of the preceding claims, in which the output circuit means comprise electronic switching elements the firing angles of which are determined by the outputs of the filter channels.

5. Apparatus according to any one of the preceding claims, in which each filter channel comprises a Wien bridge oscillator tuned to a predetermined frequency band and an associated rectifier arranged to provide a directcurrent output proportional in amplitude to the amplitude of the input signal in said frequency band.

6. Apparatus according to claim 4 and claim 5, in which a ramp signal generator generates a ramp signal which is compared with the direct-current outputs derived from the filter channels to generate pulses the phase of which is dependent upon the amplitude of said filter outputs.

7. Visual display apparatus substantially as herein described with reference to and as shown in the accompanying drawing.