Audio Engineering Society UK

Title: An interview with Neville Thiele
Location: Royal Academy of Engineering, London
Description: Special Lecture: Interview conducted by Keith Howard
Start Time: 18:30 for 19:00
Date: 24th November 2009

Download audio recording of lecture (24MB MP3)

An excellent Tutorial by Neville Thiele can be found here (AES Members only, log-in required for www.aes.org)

Abstract

Neville Thiele’s name is known to anyone who has ever taken an interest in the practical design of moving coil loudspeakers, through the Thiele-Small parameters that bear his name and that of Richard Small. In 1961 he wrote a seminal paper on the design of vented (reflex) loudspeakers that – although it was largely ignored for 10 years until reproduced in the AES Journal – is now acknowledged as initiating the filter parameter based approach to loudspeaker analysis and synthesis which today is routinely used by the audio industry at large. In recognition of this, in 1994 he was awarded the AES Silver Medal.

In this interview-based lecture, Neville Thiele will talk about what led up to this breakthrough and its significance to the speaker design process. He will then give three short presentations on loudspeaker-related topics: filter-assisted bass alignments and novel crossover approaches; driver ageing effects; and driver impedance correction in crossover networks. Questions will then be invited from the audience.

Title: ‘The anatomy of a modern audio-video amplifier’
Location: Royal Academy of Engineering, London
Description: Lecture by John Dawson, Arcam
Start Time: 18:30 for 19:00
Date: Tuesday 10th November 2009

Download audio recording of lecture (14MB MP3)

A modern Audio-Video amplifier/receiver (AVR) is an exceedingly complex piece of consumer electronics, requiring expertise in many aspects of analogue and digital audio and high definition video, plus considerable software skills. As such it represents a huge project for any small to medium sized audio company. This lecture takes a look inside the Arcam AVR600 – one of the few such units developed outside of the large Japanese CE companies – and will discuss some of the design choices made in order to try to ensure a good chance of commercial success.

Title: ‘From hi-fi to PA: predicting and measuring what we hear’
Location: Royal Academy of Engineering, London
Description: Lecture by Peter Mapp, Mapp Associates
Start Time: 18:30 for 19:00
Date: Tuesday 20th October 2009

Download MP3 recording of this lecture (24MB)

Everyone wants ‘high quality’ sound – but what does this mean – is sound quality measureable? is it predictable? The talk will look at how we can assess sound quality – both in large spaces such as concert halls, cathedrals and even railway stations as well as in small rooms such as home theatres and hi-fi listening spaces. After introducing a number of parameters and concepts that affect sound quality and the listening experience, Peter will discuss how these can be measured and potentially predicted. In particular the use of 3D computer modeling of rooms will be highlighted together with the importance of bass frequency reproduction. A number of case studies and examples of problem sound systems/rooms will be presented. Peter will conclude the talk with an insight into some of his latest research and the introduction of a new measurement/assessment concept, SQI – the Sound Quality Index.

Title: ‘How to make a high-resolution record label’
Location: Royal Academy of Engineering
Description: Lecture by Philip Hobbs of Linn Records
Start Time: 18:30 for 19:00
Date: 9 June 2009

Philip Hobbs

The New HiFi

High Resolution Music and the next generation of enthusiasts

9th June 2009. Held at RAE, London.

Philip Hobbs

Phillips Hobbs is a Producer and Audio Consultant at Linn Records Ltd. He first worked for Linn in 1982, leaving to study on the Tonnmeister course, returning to Linn in 1987 after graduating. Philip’s main roles at Linn have been in music recording and speaker design. Philip described himself as being the ‘worst sort of communicator’, because, according to him, he is both ‘Scottish and an engineer’.

Philip talked tonight of how Linn’s business has been ‘transformed over the last 3 years’ by the introduction of their music download service, a service where the customer can choose the download quality all the way to 192kHz, 24bit and where all the downloads DRM-free.

Linn History

Phillip gives a ‘two minute trip down memory lane’ of how Linn started

Linn was founded by Ivor Tiefenbrun as an offshoot of Castle Precision Engineering, a machining company who made parts for such things as aircraft and Rolls Royce. The original home of Linn, Linn Business Park gave Linn it’s name, and Linn established it’s HiFi  pedigree with the Linn Sondek LP12, a record player still in production today.

Linn expanded it’s product range and has made amplifiers, CD players, active loudspeakers and Digital Stream Players which stream files from hard disk.

Linn The Record Label

Like many other hardware manufacturers, Linn developed an interest in the recording industry. The initial motivation was to make recordings to test the reproduction capability of the LP12 and to investigate vinyl cutting lathes to the same end, but Linn has subsequently blossomed into a serious audiophile record label with many original recordings.

Traditionally focused on classical music, Carol Kydd was the first Linn ‘proper jazz artist’ and Linn released her first album in 1983. Linn made an initial pressing of 7000 records, selling them through record shops. In 1984, Linn hooked up with a  band called Blue Nile, releasing their first album ‘A Walk Across the Rooftops’. Blue Nile were keen to sell lots of records and Linn ’spent hundreds of thousands trying to get them to release their second album’. Philip, who was designing speakers for Linn at this time, estimates the total bill in relation to Blue Nile to be just under £1 million. By 1992, Linn were working on building their classical catalogue in the ’standard boutique label’ philosophy by focusing on recording quality.

By 2006, Linn had around 250 titles and had established distribution in Japan and America. In Philip’s words, the business ‘was a complete catastrophe’, as it was ‘not economically viable to sell CDs in commercial retail space’, a trend, according to Philip, that had been developing since the 1990s. Philip recalls that the situation had become so bad by 2006, Linn were faced with a decision either to leave the record business altogether, or to find some radical new approach – to find ‘a way to get back to the customers’ avoiding ‘the frustration that traditional retailing gives to many companies, and record companies in particular’, namely that ‘the company is so far away from the people they’re selling to’.

Download Revolution

The conclusion at Linn was that they needed to use the internet ‘to connect directly to the customers without compromising on quality’. At this time, Apple’s I-Tunes service was well established and, thanks to the widening availability of fast broad-band services, the ‘possibility you could sell someone 1GB of data’ was becoming a reality.

So Linn built a web site where customers could download music directly – similar to the I-Tunes idea, but with a unique selling point – the ability to provide downloads up to 24-bit 192khz sampling rate (and loss-less), where the customer is free to choose the download resolution/sampling frequency from studio-master down to MP3-level quality.  Like I-Tunes, customers can buy individual tracks or whole albums with the higher quality downloads commanding a higher price tag.

According to Philip, despite an initial cost of £100k, the site is now profitable after around 2.5 years of service.

Philip stated the more traditional music distribution method of physical  media in shop-retail results in around a 15-20% share of the ticket price being returned to the record label. For example, if a CD retails for £15, £2.5 for the record company would be considered as ‘doing pretty well’. With the download service which operates in the absence of ‘middlemen’, the margins increase considerably. Philip estimates that the download business returns around 80% of profit, and further,  their  profits would probably increase were they to move entirely away from physical media, (which Linn continue to support out of loyalty to a minority of, presumably similarly loyal,  customers).

High Quality Master Recordings

A key factor that made Linn’s Hi-Res download business viable was their long-term focus on making recordings of the best quality possible, a commitment which had led them to make many of their master recordings at 96kHz or 192kHz. This resulted in a ready supply of high-resolution back catalogue. This situation was, according to Philip, in contrast to many other record companies whose masters were typically made/archived at 44.1khz or 48kHz.

Customer Focus

Linn have a base of around 120,000 customers. With their focussed direct-marketing approach, a Friday evening email-newsletter often results in many £1000s or business by Monday from their download service.

Philip also points out that these direct marketing activities rarely offer significant discounts (which would reduce profits)  – usually, they are simply aimed to draw the customers attention to some new material or other works that may be similar to previously purchased material.

Download Usage – how are the customers using the downloads?

Philip sees 4 main customer types split by playback method.

• PCs with sound cards, Windows Media Player, I-Tunes etc.
• Portable Devices (I-Pods, Zune etc.)
• Burn-to-Disc – customers making CDR/DVD-R copies
• Streamed Media Players – from Linn and others – files streamed from local server

The DRM Issue

Linn considered the possibility of using DRM to protect their downloaded material, but at the time the web site was being prepared, it became clear to Linn that DRM just didn’t work sufficiently well. According to Philip, many people felt that moral arguments eventually killed DRM but wonders whether it was in large part due to an inability to make smoothly working system (and without imposing excessively limiting restrictions on the customers).

Download Formats

Offering such a wide range of download quality options has provided Linn with some interesting statistics on the decisions customers make when offered a quality/cost choice.  Despite price differentials, In 2007, 25% of purchases were of the ’studio master’ quality. By 2008, the figure had rising to around 50%, and so far in 2009, this seems to have risen further to around 70%. Of the CD quality albums downloaded, customers are showing a 50/50 split between choosing FLAC and WMA.

Additionally, of those customers who purchased studio master quality downloads, where they were offered a choice between 96kHz or 192kHz,   80% chose  the higher rate in spite of the fact that many players can’t play 192kHz!

Further, Phil is convinced that around half the customers who have purchased  studio-master quality downloads don’t currently have the playback equipment to support the sample rate/bit-depth they bought. His conclusion is that given a choice, Linn’s customers prefer to buy the best quality available. If this seems odd, there may be some logic here, and in some way maintaining the Linn tradition. The original Linn LP12 can be upgraded all the way to its current production specification. This ability to upgrade has been a Linn philosophy, at least for the LP12, for many years. By upgrading the equipment, the customer can benefit without buying into a whole new format. If the customer buys the Studio Master, the data they get is all that was recorded – it is essentially ‘as good as it will ever be’ – and with such a music collection, future equipment upgrades may offer further sound improvements when replaying the original material, in many ways similar to vinyl.

High Resolution Benefits

Philip made an impactual demonstration of the potential enjoyment offered by high resolution and high quality recording by playing Handel’s Messiah conducted by John Butt (and where Philip was himself the recording engineer). Unbeknown to the audience, the recording began at rate of 88.2kHz/ 24-bit, but as playback progressed, the bit rate dropped to 44.1khz 16 bit, then to 192kb mp3, then to 96kb, mp3. Although these differences were not immediately obvious to all, (at least in the listening environment in which they were presented), Philip described how it was common for the listeners attention to progressively drift to other matters as the bit-rate dropped, they ‘tend to get bored and start thinking about something else’. This certainly described my personal experience with surprising accuracy.

Streaming Player

Philip briefly demonstrated one of the Linn Streaming Players which offer one possible method of replaying the downloaded material. One of the benefits Philip sees for customers with this type of equipment is a significant increase in convenience. Gone are the walls of CD/LP shelves, replaced by a compact hard-disk-based server and controlled via a little application on their I-Phone, a use case Philip describes as ‘addictive’.

The Future

Linn are beginning to diversify. They have taken on a couple of small labels and are offering downloads for them alongside their own material. For those interested in purchasing downloads, Linn’s web site may be found at http://www.linnrecords.com/ and test files for evaluating quality (and compatibility)  can be found at http://www.linnrecords.com/linn-downloads-testfiles.aspx

The AES would like to thank Phillip for his fascinating talk. I’m sure many members were greatly encouraged to hear that there are still many customers for whom recording quality something worth paying for.

Report by Nathan Bentall

Edited by Keith Howard

Title: ‘Critical listening/evaluation – a path to the future of quality music’
Location: Royal Academy of Engineering, London
Description: George Massenburg of George Massenburg Labs
Start Time: 18:30 for 19:00
Date: 3rd June 2009

George Massenburg needs little introduction – even if you don’t know of him, you have probably heard his recordings. For a detailed biography, see www.massenburg.com/cgi-bin/ml/bio.html.

Meeting Report

Quality recordings

What is difficult to represent in this report is the passion George exudes about music, a passion which drives him to strive (and help others to strive) to continually improve the quality of recorded music. Many recordings were replayed in the course of this lecture, some made by George, others not. Most were 192kHz, 24-bit; some were transferred from analogue master tapes.

George began by replaying a Diana Krall track, pointing out the subtlety and detail captured by Al Schmitt. In a change of style, the next track was by Neil Young – a new song about the recent financial crisis with the chorus line “A bailout is coming, but not for you”. Elements of the recording were described, there being a pair of guitars (slide and acoustic), rock’n'roll drums and a hi-hat “somewhere in the background”.

George then played a clip from YouTube of a recent and currently very popular track by Autotune The News (their second track, pirates. drugs. gay marriage), an original piece where television newsreaders have been cleverly edited in time and pitch such that they appear to be singing. The point here? Although the YouTube clip has been extremely popular (it received 1.5 million hits in the first week, possibly setting a web record), and although George admitted to thinking it “brilliant”, the audio quality is very poor. George pointed out that repeated listening at this YouTube-quality quickly gets very annoying because of the low-fidelity sound.

Compression Artefacts

George then played the results of some subtraction tests on lossy audio codecs, a technique which George refers to as the Moorer test as it was originally suggested by James A Moorer. In these tests, high-quality 192kHz, 24-bit recordings were converted to various encoded forms such as MP3 and AAC. The encoded files were then decoded and upsampled back to the original 192kHz, 24-bit. A sample-by-sample subtraction was then performed, and the resultant difference – the error introduced by the codec – then replayed. The resulting error signal is surprisingly high in amplitude (estimated by George as typically 25-30% peak), clearly correlated to the signal and with a complex relationship to the original sound (not simple harmonic distortion).

George takes the view that his students should learn to recognise the nature of the codec error using this subtraction method and then listen to the encoded music. Using this learning technique, listeners can familiarise themselves with the artefacts’ sound in isolation, and can subsequently pick them out more readily when the encoded material is played.

Listen Again

George believes that every time we hear a piece of music we should have the possibility of hearing something new – “to take home something else” – and that this is more readily achieved with high resolution recordings. Although George concedes that it’s possible to make a “pretty good” 44.1kHz/16-bit CDs, he remembers the first time he heard a digital recording: rather than being impressed, he was “horrified”.

Subsequent work to push the boundaries of converter technology (George recalls the contribution of Paul Frindle in this area) has convinced him that good digital now is good. He believes that we don’t have to go back to magnetic tape to make good records, and describes himself as having “an easy peace” with both vinyl and analogue tape.

Recording Tips

George deprecates recording techniques in which small elements are recorded separately and later combined/corrected/stretched/re-tuned, etc. He believes a key to great music recording is to maintain a performance focus. Preferably, the band should perform and be recorded playing simultaneously in the same space. George offers these suggestions to help your next recording:

• 1) Only use destructive record.
• 2) No punch-ins.
• 3) No one is allowed to take the recording home and ‘tweak’ it – they can do another take, but the previous one will be overwritten.

The AES UK section and George wish to thank the companies who kindly supplied equipment for this lecture, namely ATC (monitor loudspeakers), Digidesign (ProTools system), Arcam (DVD player) and Prism Sound (D/A converters).

Report by Nathan Bentall (edited by Keith Howard)

Title: ‘Grand Designs – Networked DSP for Really Big Buildings’
Location: Royal Academy of Engineering, London
Description: Michael Page of Peavey Digital Research
Start Time: 18:30 for 19:00
Date: 14 July 2009

Download MP3 audio recording of this lecture (18MB)

Download PowerPoint slides of this lecture (6MB, MS PowerPoint 97-2003 compatible)

Abstract

Advances in audio distribution and control over digital networks have delivered tremendous benefits for operators of large venues and premises, such as theme parks, cruise ships, stadiums, live performance venues, airports and industrial complexes. Audio for entertainment attractions, background music, paging systems and evacuation purposes may all be transported and controlled on a single distributed system, via Ethernet and IP local area networks. Audio processing for acoustic correction, routing, mixing and other processes is all easily performed using programmable DSP, located both centrally and at distributed nodes. Michael Page of Peavey Digital Research will discuss and demonstrate the technology used to achieve this.

Meeting Report

Michael started his talk by listing the range of applications for the networked audio DSP systems he’d come to talk about: a diverse range including airports, stadiums, theme parks, ports, houses of worship, legislatures, and convention centres. Then, displaying an aerial view of the truly gigantic Hartsville-Jackson Atlanta Airport, he posed the question: what does it take to wire an airport for sound?

It sounded like a straightforward question, until Michael started discussing it. He started by talking about the audio system outputs: each boarding gate area (all 179 of them, at Atlanta) needs an individual output, each lounge, each concession, each arrivals hall zone, each check-in zone, each customs hall, each luggage reclaim zone… not to mention all the non-public areas. Each of these many hundreds of outputs needs, in addition to level control: EQ for loudspeaker correction, EQ for room correction, delay for time-alignment, possibly dynamic range processing, and possibly ambient level sensing. Ambient level sensing is a particularly complex DSP function: it uses a measurement microphone to detect the ambient level in a space, so that the level of the loudspeakers can be adjusted to ensure a consistent signal-to-ambient-noise ratio for the listeners. But if the audio system is active while this measurement is being made – as is often the case – sophisticated DSP is needed to “null-out” the contribution from the loudspeakers from the signal picked up by the microphone, in order to obtain an accurate measurement.

Next, Michael considered the inputs. Each boarding gate has a paging station, plus paging stations for every lounge, concourse and information desk, that may be routed to any system output. There may be background music inputs for lounges; automated message playback systems (“Please do not leave your bags unattended”, etc.); automatic announcements from the fire alarm system; and all these need to be prioritised, so that evacuation announcements aren’t blocked by the background music, for example. Each input typically needs EQ and dynamics processing, and needs to be routable or mixable to any combination of the several hundred outputs. So: we’ve got an audio system with several hundred inputs, several hundred outputs, all connected with a giant intelligent mixer, and a sizeable amount of DSP on every input and output. The inputs and outputs are distributed over six huge buildings, across a site a mile long and half a mile wide, and it has to integrate with the security, life safety, building management and enterprise management systems. Finally, it needs to be extremely robust and redundant, so that it keeps running even if the system sustains major component or infrastructure failures, perhaps caused by a large fire or a bomb explosion. Wiring this for sound isn’t as simple as first thought!

Michael next considered another application: stadiums need to get high-quality sound to every seat in the stadium, despite huge acoustic differences in the seat and loudspeaker placements. So each block of seats needs separate loudspeakers and processing – plus zones for all the internal areas: locker rooms, bars, restaurants, VIP areas, conference centres, car parks, atriums, etc. Stadiums don’t need as many inputs as an airport, but the ambient level processing is even more critical due to the difference in ambient level between sides of the stadium, at crucial points in events!

Finally, Michael discussed the requirements of theme parks. Audio-visual experience attractions such as “Terminator 2 3D” at Universal Studios are an obvious application: audio is a fundamental part of these attractions, and they require high-level, high-quality audio reproduction from a large number of independent channels to be precisely synchronised, sometimes interactively, with the motion control and video control systems that create the other dimensions of the visitor experience. Audio reproduction, even if it is only zone-specific background music, is usually present at pretty much every publically-accessible location in a theme park, and all public areas must have audio coverage for life safety announcements such as fire evacuation. As with airports, the wide range of different acoustic environments and geographic spread requires a large number of independently-addressable audio zones. The audio system inputs may be local, such as interactive audio playback within rides, or remote, such as background music, advertisements or paging announcements. Parade grounds and live shows complicate matters further, with many radio microphones and loudspeakers covering a very large area.

Now the problem is understood – how is it solved? Traditionally, it was analogue: large quantities of analogue multicore, thousands of crosspoints of punch-on patchbay, and many racks of analogue signal processing. It was difficult and expensive to engineer robust system redundancy, and very difficult to get computer-interfaced control of the audio signal processing. Each audio channel required a balanced line connection, requiring a huge quantity – and weight – of cable.

All this was revolutionised in the early 1990s by the arrival of DSP technology. DSP brought huge cost and functional benefits to the audio installation industry, for two principal reasons: it allows very simple interfacing of audio functionality to computer systems; and it permits arbitrary, heterogeneous arrangements of audio DSP functionality to be realised cost-effectively in generic hardware. The other crucial development from digital audio technology was digital audio networking, carrying many channels of uncompressed audio at low latencies on standard computer networking infrastructure. Analogue audio multicore cables were hugely expensive to buy, and even more expensive to install, whereas computer networking cables are flood-wired into all commercial and public buildings. So despite the relatively high transceiver costs, audio networking was a vastly cheaper way of getting audio around a commercial building. It also implicitly provided computer-controlled audio signal routing, saving the cost of expensive dedicated audio routers. The de-facto standard audio networking technology for the commercial installation industry has been CobraNet since the late 1990s, which is Ethernet-based (layer 2), has a latency of about 5 milliseconds, and convey up to 64 channels of audio in both directions.

To indicate the state of the art in audio networking, Michael spoke about a relatively new technology called Audinate Dante. It’s Internet Protocol based, typically runs over Gigabit Ethernet, and it’s scalable for both bandwidth and latency, making it very flexible for a wide range of applications. It may be configured for performance comparable to CobraNet, but in principle it can also function (with higher latency and lower bandwidth) over poorer-quality networks such as the public internet, or alternatively it can function as an ultra-low-latency, ultra-high-bandwidth point-to-point link between audio processors.

Michael then explained how these technologies are brought together. A system typically comprises some number of analogue audio i/o units, DSP units and control interfaces, connected by an Ethernet network for audio and control data, but these units may all be physically remote from each other. Control interfaces are used to communicate with user interface devices, uninterruptable power supplies, fire and life safety systems, building services management (HVAC) systems, show control systems, and many other possibilities.

This is a very successful technology area, with a number of companies actively competing. Peak Audio developed the first product of this kind in the early 1990s, the MediaMatrix system, which comprises a PC-AT motherboard with custom ISA backplane, DSP ISA cards with Motorola 56K DSPs, and analogue i/o boards. This was first used to provide an adaptive, distributed sound reinforcement system in the US Senate Chamber, which posed some unique challenges that could only be solved by computer-controlled DSP. The MediaMatrix product was licensed to Peavey, who manufactured and distributed it, and it was extremely successful.

The second generation MediaMatrix product was the Nion, launched in 2004. It has a PowerPC CPU running embedded Linux, for distributed control and communications with the other Nions on the network, and monitoring the DSPs and audio interfaces. It has a number of Analog Devices SHARC floating-point DSPs, a proprietary high-bandwidth low-latency audio link bus that uses Cat-5 cable to connect Nion units together, and a CobraNet interface module. CobraNet has such high bandwidths and low latencies that it needs dedicated data processing hardware: a generic CPU doesn’t have sufficient network performance. It also features a selection of “general purpose I/O” connections for control interfacing: logic i/o, relays, high-current outputs (for driving lamps, solenoids, etc.), control voltage inputs and outputs, and rotary encoder connections, for creating simple custom control panels.

Michael demonstrated of the NWare software, a Windows application used for defining the DSP and control functionality. It has a graphical user interface resembling a CAD drawing tool, allowing the user to drag-and-drop blocks representing DSP functions, audio i/o, control functions, control scripts, and many other functions. It also allows creation of custom control panels for PC-based or touch-screen user interfaces. When the design is complete, the “deploy” button is pressed to generate the DSP and control code, and download it to Nions connected on the network, which immediately take on the designed functionality.

The lecture was wrapped up with a look at the NWare system design for the MediaMatrix system at Emirates Stadium. As well as huge quantities of signal processing blocks, it featured touch-screen graphical user interfaces based on architectural plans of the stadium for ergonomic control and monitoring of audio across many different zones in the stadium at once. Custom support for communicating with UPS devices is implemented in the Python scripting language, which executes on the Nion. This vast system design gave a flavour of the tremendous complexity of the audio system implemented with MediaMatrix.

The NWare software can be downloaded for free from the downloads section on the MediaMatrix website.

Meeting report by Michael Page