This technical visit is now full!

A technical visit has been arranged to ATC Loudspeaker Technology in Stroud, Gloucestershire on Friday 16th July, offering AES members a rare opportunity to see first-hand how these very highly regarded speakers are designed and built right here in the UK .

The visit will start at 11:00 and finish around 16:15. ATC are also very kindly providing refreshments and lunch.

ATC is a specialist British manufacturer of loudspeaker drive units and complete sound reproduction systems. They design and manufacture loudspeaker drive units and systems to achieve levels of performance far in excess of the industry norm which is achieved by adopting a thoroughly professional engineering approach to the issue of basic design, materials science and production technology.

The visit will include a tour of the design and production facilities and demonstrations of their products.

The number of places is strictly limited, so book your place early to avoid disappointment.

To reserve your place, please ring Heather on 01628 663725 or email uk@aes.org.

Abstract

Stadium sound systems are always complicated projects. There is the need to deal with filling large spaces with sound and the requirement to comply with the many (and conflicting) voice alarm regulations.

Roland Hemming will explain the story behind the new sound system at Lord’s cricket ground. It uses the latest audio networking technology, a brand new signal processor and it involved unprecedented co-operation between two manufacturers. He will also explain how he deals with project risk and with the complexity of doing the work in many phases and with the fact that the ground is in a residential area.

About the presenter

Roland Hemming has established himself as one of the leading independent audio consultants and project managers for large technical installations.  His wide experience ranges from live events to construction sites, from manufacturing to installation, from cruise ships to theatre, rail, corporate AV, broadcast, education and stadia.  He has managed a number of very large projects including the Millennium Dome, Ascot Racecourse, Twickenham Stadium and St Pancras station.  He is also a consultant to manufacturers on the development of forthcoming audio products and is helping to develop and introduce the next generation of audio networking systems.

EMI has an archive going back to 1898 and, since Abbey Road Studios opened in 1931, there has been a gradual increase in the remastering of that back catalogue for new formats. Starting with a potted history of EMI, the early years of recording and the work of Alan Blumlein, we move on to the emergence of remastering at Abbey Road and the systems and techniques used today. The talk will then concentrate on the use made of CEDAR Audio’s Retouch software in the audio restoration of The Beatles album remasters as well as its more usual use in the creation of music for the video game The Beatles Rockband. Along the way we will hear rare audio extracts from EMI’s archive and clips from The Beatles’ recordings to demonstrate these remastering and restoration techniques.

Abstract

The practice of processing audio signals to impose lifelike room acoustics on them for headphone presentation is called auralization. The two most commercially exploited applications of auralisation are the conversion of headphone stereo listening into an experience more like loudspeaker stereo listening, and the simulation of proposed architectural spaces.

Although the tools required for auralization are fairly well understood, experiments that test the response of the human auditory system to spatial cues are generally designed to investigate one changing parameter in complicated sound field, and the way in which stimuli are synthesised is not standardised. These limitations mean that little has been written recently of the ways in which the various parts of the human auditory system interact to experience a spatial illusion presented over headphones.

This talk presents, informally, some observations learned from several years’ experience trying to analyse and deceive the spatial parts of the human auditory system. It discusses how we perceive the spatial cues present in direct sound and reverberation that are central to auralisation, and the most effective and efficient ways of presenting a convincing illusion without causing listening fatigue.

An active acoustic absorber must sense the sound field in a space, and generate a signal to absorb energy from that field. In 1-D such absorbers work very well in situations such as ducts, and in 3-D systems they are effective if source and canceller are much closer than a wavelength. In actual rooms with loudspeakers, such conditions never apply. A tutorial is presented outlining the known theory and possibilities of active absorbers that work over a wide band. The self-pressure of the absorber complicates its operation, and an analysis is presented in which this self-pressure is cancelled by a signal related to cone motion. The resulting device may still suffer from implementation problems. Experiments are discussed that determine the required microphone signal that needs to be applied to the adjacent absorber driver. Active absorbers can also act as subwoofers. To conclude the talk, some FDTD calculations are presented which show how a subwoofer excites room resonances, and the influence of different configurations. Delay-and-cancel techniques lead to a very flat bass response, but that probably removes too much of the room acoustics.

Download recording of lecture here (20MB MP3)

Lecture Report

Dr Emmett opened the lecture by summarising the audio-video synchronisation challenges encountered when putting together a television programme. It is better to correct synchronisation problems as they occur in the broadcasting chain than to attempt to correct them all immediately prior to transmission, as the former practice greatly simplifies video editing. With this achieved, attention turns to keeping audio synchronised during broadcast transmission and reception. This is particularly important for human speech: humans are exquisitely sensitive to lip sync. We develop this facility almost as soon as we can see, and the psychological need for lip movement to be attached to speech is so great that each Dalek must display a light that pulses in sync with speech, in order to bond dialogue to a particular character.

A number of techniques were employed in the days of purely analogue transmission to ensure that audio and video were kept in sync. It was not unusual for a programme’s video signal to be relayed via satellite and its audio via telephone, and a compensating audio delay had to be inserted to offset uplink and downlink delays. An example of this was used in ITN in the early 1980s. An in-band masked ‘bong’ was timed to follow any video cut in the programme by exactly one second. It was possible then for engineers to adjust the audio delay manually to maintain sync, even where this varied during the programme. Similar timestamps must still be maintained in digital systems, although this facility is now generally accommodated within the channel code.

It is increasingly common for audio and video to be streamed by piggy-backing on a packet-based protocol and transmitting via existing IT infrastructure. This works as long as there is sufficient bandwidth. Otherwise, heavy-duty interleaving is required to compensate for dropped packets, which increases transmission delay, and the chances of sync loss and system failure. As with real piggy-backs, the heavier the payload, the slower the system, and the greater the likelihood of collapse.

Consider what the word ’standard’ means: this is where problems are compounded. The word has two distinct meanings. It can refer to an outgoing or obsolescent paradigm (such as ’standard definition’), or to standard-bearing in its original sense — at the technological vanguard. We frequently encounter problems when it is necessary to choose between a plenitude of competing standards of different ages, some of which have yet to be adopted, and many of which should not. Standards are necessary only when the current best practice is unclear, so clues for choosing ‘good standards’ were suggested. A good standard must be fit for purpose, timely, and robustly defined: if the plug fits, the signal should work. There are also caveats, because not all standards are intended to be friendly (DRM systems were cited as an example), and even de facto standards undergo sudden and complete changes. Finally, although a standard needs to be owned by a company or committee to avoid obsolescence, it should contain no element for revenue generation.

The emergence of competing delivery standards in broadcasting has brought the synchronisation problem into the home. Many digital multichannel audio transport layers can be conveyed over S/PDIF channel code using IEC 61937 (Dolby Digital; DTS; linear PCM), and a home cinema amplifier may typically accommodate sixty connectors and a dozen multichannel formats. As for the picture, high-definition video formats such as 720p and 1080p co-exist with conventional 625-line 4:3 and 16:9 broadcasts. There are a number of video interconnection formats with different costs, advantages, and limitations. Any of four digital video broadcasting standards are in use in different regions throughout the world, encompassing several standard frame rates. Meanwhile, individual consumer products are designed for world markets, and are simultaneously compatible with many of these standards. In fact, UK broadcasters have been unable to rely on viewers possessing ’standard’ receiving equipment since 625-line broadcasts began in the 1960s.

Now that it can take half a day for a professional engineer to set up a new television, it is quite likely that a set-top box in a typical home may be configured to down-convert 720p video to standard definition, and transmit this signal over RGB SCART to a plasma television, which will then up-convert it to 1080p. Audio-video synchronisation is then at the mercy of equipment manufacturers.

Dr Emmett summarised his lecture with advice from Antoine de Saint-Exupéry: ‘No design is finished until the last superfluous item has been removed.’

Report by Ben Supper