GB2434067A

GB2434067A - Low latency monitoring in audio mixing

Info

Publication number: GB2434067A
Application number: GB0600103A
Authority: GB
Inventors: Nigel David Horspool; Andrew Robert Parker; Paul Edward Hanham
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-05
Filing date: 2006-01-05
Publication date: 2007-07-11
Also published as: GB0600103D0

Abstract

For musicians monitoring the audio they create, a critical feature is latency i.e. the delay between a note being played and when it is heard, e.g. over headphone or loudspeaker monitors 5. If a computer 1 is used to perform processing of the audio stream from various sources e.g. instruments or microphones 4, as well as providing monitoring outputs, this may increase the latency above an acceptable level. Direct monitoring, i.e. before processing in the computer 1, requires monitor output devices for each source and thus increases hardware costs. The disclosed arrangement aggregates several sources and provides direct monitoring at low latency. Multiple audio interface devices 3 are connected by a standard bus 2 and receive inputs from the various sources 4. The interface devices 3 sample the analogue inputs, which are sent via the bus interconnection 2 to computer 1 for processing, mix their inputs and send back the mixed audio to appropriate monitors 5, thus avoiding latency generated in the processor 1. Some processing may also be provided in the interfaces e.g. reverberation effect for a guitar, or mixing of audio stream from other interfaces, such that one interface generates a mix of all the sources for the processor 1. The bus may be USB or Firewire (R.T.M). In the latter case one interface 3 may configured as a master which provides the full mix, or the master function may be distributed amongst several interfaces (Fig. 3 not shown).

Description

I

LOW LATENCY MONITORING FOR MULTIPLE DEVICES

The invention relates to audio interface devices that allow musicians to connect instruments to a computer via standard interface buses such as Firewire and the Universal Serial Bus. The computer (PC or Macintosh) performs numerous functions on the data including mixing of multiple audio channels, application of audio effects, recording the resulting data to disk and transmitting it back to the audio interface device to be output to speakers or headphones.

Musicians need to monitor the music they are generating, and the rest of the group are creating. A critical feature for correct operation is the time taken, or latency, for a note created by the instrument to be heard by the musician. This latency must be below a certain threshold, typically below 10 milliseconds.

The monitoring can be done by two methods; firstly using the computer to mix the different audio channels, secondly using the audio interface device using a technique called direct monitoring. Using the computer increases the latency, but provides more flexibility since it can aggregate audio streams from a number of interface devices.

Direct monitoring is lower latency since the mixing is done by the audio interface device and the resulting stream is output directly to the speakers / headphone output, without being transmitted to the computer via the USB or Firewire (fZ.T. cM.) OUSb.

The two methods above both have disadvantages; using the computer can increase the latency above an acceptable level especially when adding lots of effects, while the current direct monitoring is only applicable to single audio interface devices, so users must buy expensive devices when they need many input and output channels.

An object of this invention is to provide a method to aggregate a number of audio interface devices, providing direct monitoring which does not use the computer to mix streams from multiple devices.

Accordingly, this invention provides an audio interface device that provides the normal device functions, but also contains the capability to mix multiple input audio channels to a combined stream which is output to one of the plural devices that provides a master mixing function; it mixes the combined streams before transmitting the final mixed audio stream back to each device to be output to speakers or headphones. The invention provides a method for ensuring that each device is synchronised to a common time stamp and that the correct audio samples are combined.

A prefer embodiment of the invention is to use the peer-to-peer capability of the Firewire bus to allow transfer of data between devices without PC / Mac intervention. The invention also defines that each device can optionally perform aggregating multiple audio streams onto a reduced number of Firewire channels, thereby allowing more devices to be connected to a computer that supports a limited number of Firewire channels.

A preferred embodiment of the invention is to allow any of the audio interface devices to perform the master mixing function.

Preferably, the master mixing function can be distributed amongst a number of the interface audio devices when the number of devices increases, thereby removing the need to have some devices requiring extensive processing functionality.

FIGURE 1 shows an audio interface device connecting musical instruments to a computer.

FIGURE 2 shows how multiple audio interface devices can be connected using a standard Firewire bus, or Universal Serial Bus.

FIGURE 3 shows a configuration where the master mixing function is distributed across a number of interface devices.

As shown in Figure 1, an audio interface device (3) is used to connect instruments to a computer (PC or Macinitosh) (1) via a standard interface bus (2). The instruments (4), for example guitars, drums, micronphones etc, connect to the interface audio device through analogue connections. The audio interface device samples the notes from the instruments to create discreet digital samples using an analogue to digital converter. The computer can transmit a mixed stream back to each interface device which output them to speakers or headphones (5).

As shown in figure 2, multiple audio interface devices (3) can be connected using a standard Firewire bus (2). The computer (1) can combines these devices so that they appear as a single device to users, allowing a single control panel to control all devices.

As shown in figure 3, the master mixing function (is distributed across a number of interface devices (3). Each device mixes the input audio channels into a single stream (7) and outputs it across the Firewire bus (2) to the master mixing device (6). The streams are combined, then sent back to each device (8) so that the combined stream can be output to speakers or headphones. Optionally each device can apply audio processing functions on the data before or after mixing; for example an audio stream from a guitar could have a reverberation audio effected applied prior to mixing with other audio streams.

Claims

CLAIMS

I. An audio interface device that has the ability to provide direct monitoring for a number of units with the mixing performed by a combination of all interface devices and not the computer (PC or Macintosh), thereby providing low latency monitoring of all audio channels.

2. A method of direct monitoring using multiple devices using the Firewire bus with each device providing mixing of input audio channels and outputting the resulting stream across the Firewire bus to one of the audio devices using peer to peer capabilities, the multiple streams combined into a single stream by one of the units which then transmits it to all devices so that the mixed audio can be output to speaker I headphone outputs.

3. A method of defining which device will mix streams from other devices, either through manual configuration (for example a user configured switch) or automatically by negotiating the master via the Firewire bus.

4. A method of devices receiving audio streams from other devices and aggregating the multiple audio channels onto a single Firewire channel, thereby allowing a large number of devices to be connected to a PC or Macintosh which support a limited number of channels.

5. A method of optionally adding a time code to each mixed streams so that the correct samples are mixed, even when the audio channels come form different sources (eg one source could be the computer).

6. An alternative method to provide aggregation and direct monitoring using the same techniques described by claim 2, but using a dedicated interface bus or a Universal Serial Bus interfaces rather than the Firewire bus.

7. A method of creating systems that can decompress compressed audio streams or apply extra processing to multiple streams using a number of lower cost devices connected via a Firewire or USB bus, allowing the total processing requirements to be split over a number of smaller cheaper processing units.

8. A method of defining which device will route different parts of the audio data stream to other devices, either through manual configuration (for example a user configured switch) or automatically by negotiating the master via the Firewire bus 9. A method for ensuring that each device is synchronised to a common time stamp and that the correct audio samples are combined.

10. A method of providing multiple device direct monitoring as claimed in Claim I with the additional ability for devices to apply audio processing functions on the data before or after the mixing with other data channels.

11. A method of providing multiple device direct monitoring as claimed in Claim 1 with each device combining audio data from different audio interface including, but not exclusive, analogue audio data, MID! data, S/PDIF data and audio data sent from the computer.