GB2427107A

GB2427107A - Radio microphones and wireless musical instruments with multiplexed digital channel

Info

Publication number: GB2427107A
Application number: GB0511640A
Authority: GB
Inventors: Howard Thomas; Paul Hirchfield; David Lockstone; Subhash Sharma
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-06-08
Filing date: 2005-06-08
Publication date: 2006-12-13
Also published as: GB0511640D0

Abstract

Radio mics and wireless musical instruments digitise the recorded sound and then transmit it over a time multiplexed radio channel. Synchronisation of the channel is by a synch pulse transmitted from the radio receiver. The system may utilise a direct sequence spread spectrum (DSSS) channel for enhanced noise immunity and the sampling and quantisation of the ADC's and DAC's may be adjusted to allow a trade off between sound quality and number of channels. The system overcomes the need for 1 receiver per microphone associated with analogue systems and can eliminate the cabling requirements in recording studio applications.

Description

Multiple Audio Channel Digital Wireless Microphone and Musical instrument

System Outline of document This paper describes a novel approach to Wireless Microphone and Musical Instrument Systems. As these systems are available on the market today from several manufacturers, this paper is structured to: 1) Explain how current systems work; 2) Explain the novel attributes of the invention described in this paper This document includes diagrams and claims that support the invention.

Description of invention

An Introduction to Wireless MicroDhone and Musical Instrument Systems Wireless (or Radio) microphones and wireless instrument systems are used by singers and performers in bands to provide connections normally to an audio mixer without the need for cables. This provides freedom for the performers to move about the stage (or within a studio) freely without the possibility of accidents caused by tripping over cables.

Radio microphones and instrument systems have been available for several years from a number of suppliers. However, they utilise expensive technology and use analogue techniques for both the signal processing and radio transmission. In addition, they also suffer from one major drawback - each microphone and each instrument transmitter system have to use a different single radio frequency. The result of this is that each system has to have a separate receiver tuned to that frequency. The output from each of these receivers is typically connected to the inputs on an audio mixer.

This paper proposes a new approach to Radio microphones and instrument systems. The invention described here uses digital techniques to ensure high quality audio is transmitted from the microphone or instrument but also enables a single receiver to be used with multiple transmitter units.

What is a Wireless Microphone and Instrument system? Wireless (or Radio) microphones and wireless instrument system comprises of two parts a battery powered Transmitter and a mains powered Receiver. The transmitter is either "integrated" into a microphone or it is a separate unit that can be used with any microphone as an "add on" unit. In the case of an instrument (e. g. a guitar), the transmitter is connected to its electrical output and then either mounted on the instrument or is designed to be housed in a small enclosure and worn on the body, e.g. clipped to a belt.

The Receiver is usually mains powered and its single analogue audio output is typically connected to an audio mixer.

The signal is transmitted to the Receiver using analogue FM techniques using a frequency controlled by the radio authorities.

Different music or vocal signals must be transmitted to separate individual receivers. Due to the analogue FM techniques deployed by the currently available systems, one receiver cannot work with more than one transmitter, If the individual musicians in a band want to connect DIFFERENT audio signals from a number of microphones and/or musical instruments to their mixer then completely separate transmitter units and receivers using different frequencies MUST be purchased. This is clearly not cost effective.

The new approach to Wireless Microphone and Instrument systems This section describes how the new system works and its unique attributes. It also explains how it solves the issue of having to deploy a separate receiver for each transmitted signal.

There are some similarities between this invention and the systems previously described - there are still transmitter units and receiver units. The transmitters are connected to microphones and/or musical instruments. The receiver's audio outputs are typically connected to an audio mixer and the two communicate using radio technology.

The difference between the two however is how this is done. Current systems use analogue techniques for the signal processing and radio transmission. The radio transmission uses one radio frequency which is demodulated by the receiver and the resultant signal is fed into the audio mixer. It is this analogue radio transmission method that limits one signal to be sent from the transmitter to the receiver, It is simply one frequency for each music signal.

The approach adopted here is radically different. The signal processing and radio transmission is completely digital yet deploys cost effective technology. As described earlier, this proposal enables multiple audio signals to be transmitted to a single receiver unit Thus, eliminating the expense and complication of having multiple receivers - one for each audio signal.

Diagrams number I and 2 show the actual difference from the users' perspective.

Note that in this example for each musician to transmit a different signal (signal 1 and signal 2) using the current systems, an additional receiver is required. In fact, an additional receiver is required for EACH additional user.

Detailed descriptions for this new approach follow in the next section.

Note that in this example, each musician can transmit a different signal (signal I and signal 2) to ONE Receiver. This proposal can apply to many musicians and singers each transmitting a different audio signal. It is not limited to just two signals, this is just an example. The number of channels that can be accommodated is governed by the available bandwidth of the wireless solution.

Detailed Description

The Transmitter unit.

The transmitter converts each analogue audio signal into a digital format by use of an ADC (Analogue to Digital Converter.) A header packet is added to each digital stream. This is so that each signal can be identified by the receiver for correct decoding. These digital signals are in effect multiplexed into a higher bit rate digital stream with each transmitter sending its digital signal in a ti me division multiplexed manner. (In other word, each unique transmitter sends its signal to the one receiver at a given moment in time relative to the other transmitters.

With the greater flexibility that is available using a digital approach, a range of analogue to digital sampling depth and rates can be considered giving a "quality/bandwidth" trade-off.

(However, each transmitter and the receiver must use the same bit resolution ADC and DAC.) This digital signal is then adapted to be transmitted, wirelessly to the receiver by using DSSS (Direct Sequence Spread Spectrum) technology. This proposal does not specify any particular wireless standard but can be used with a number of wireless solutions providing there is adequate bandwidth.

Using DSSS provides greater resiliency to the signal being transmitted and offers superior reception over the analogue systems. In addition, radio diversity techniques can be deployed if required to provide additional resiliency to wireless interference.

As there will be a number of transmitter units deployed, there needs to be synchronisation to ensure that only one transmitter is enabled (i.e. transmitting its digitized audio signal) at any time. Thus each transmitter must also be able to receive a sync pulse' to ensure this happens. The receiver must transmit this pulse to all the transmitters prior to each transmitter unit sending its data to the receiver in sequence and for each transmitter to be quiet' (i.e. transmitter turned off) when others are in transmit mode to avoid contention. A timing diagram is shown in diagram 4.

The Receiver unit This can provide more than one audio signal to, for example, an audio mixer and several transmitters can be used with it. Receivers can receive a single signal or, unique to this approach, different signals from multiple transmitters.

Like the Transmitter unit, the Receiver unit looks like the currently available units. However, rather than receiving one analogue signal using FM radio techniques, it receives a digital multiplexed signal from multiple Transmitters. This digital signal, as described earlier in this document carries multiple audio signals - not just one.

The Receiver has a built in DSSS receiver to match the transmitter. (In addition, radio diversity techniques can be deployed if required to provide additional resiliency to wireless interference.) The output from this is the "raw" digital multiplexed signal carrying these multiple audio signals - at this stage it is still in a digital format.

The receiver will then recover the individual bit streams and feed them to individual DACs with supporting circuitry to fully recover the audio signal. This is then output via a socket typically to an audio mixer.

As outlined in the transmitter section, the receiver must transmit a "sync pulse" to all the transmitters. This is to align the numerous transmitters prior to each one sending their individual digitised audio signal in sequence and for each transmitter to be "quiet' when others are in transmit mode to avoid contention. A timing diagram is shown in diagram 4.

Figure 3 shows a block diagrams for both the Transmitter and Receiver units.

Claims

Claims 1) Resolves the need to have multiple receivers for different audio

signals by decoding a multiplexed digital signal carrying multiple audio signals from multiple transmitters.

2) This invention takes advantage of competitively available DSSS wireless technology.

The design provides an acceptable latency performance demanded for this application.

3) As a result of this design, all transmitters use a common single radio frequency 4) By using digital technology, this enables a trade off between the number of audio channels carried (by scaling the ADC and DAC resolution) and the audio quality per channel.

5) Can evolve with the changing wireless standards and is independent of any one standard. (Note however the need for low latency, claim 2.) 6) This system can also be deployed in a studio environment to simply eliminate cables from microphones and musical instruments.