Audio testing on Meridian's F80 production line

For more than 30 years Cambridgeshire-based Meridian Audio has been innovating and crafting desirable, high-quality audio and video equipment for the home entertainment market. Founded in 1977 by Bob Stuart and Allen Boothroyd, the company has won numerous accolades for product performance and design, including an unprecedented three British Design awards.

In 2005, Meridian Audio began a unique collaboration with car manufacturer Ferrari to develop a range of products that reflected the unique qualities of both companies. Ferrari's reputation for producing high-performance and desirable GT cars, as well as running a record-breaking Formula One racing team, is well established. However, the company also has a world-leading reputation in the field of materials and composites technology, which perfectly complemented Meridian's expertise in digital audio innovation. Both companies share a pedigree of performance and elegant design.

The Meridian F80
The result of this partnership is the Meridian F80, a transportable home entertainment system that is small and stylish, yet incredibly powerful and versatile. Badged with Ferrari's Cavallino Rampante and the distinctive Meridian 'M', the F80 has received rave reviews from consumer and trade journalists alike for its style - it won What Hi-fi's Best For Style award - and its exemplary audio performance. UK motoring magazine Evo, for example, noted that the F80's shell material, developed in collaboration with Ferrari, "keeps vibrations to a minimum, enabling it to deploy its thunderous 80-watt output to maximum effect", while on-line audio and AV magazine The Perfect Vision described the F80 as an 'audio powerhouse' and 'a marvel of engineering and performance that sets a new and outrageously high standard for integrated entertainment systems'.

For Meridian, achieving outstanding audio quality was a key requirement from the outset. The company recognised that, in order to do this, it needed equally high performance audio test equipment, both in its R&D labs and on its production line.

Paul Holmes, Meridian's Test Manager charged with designing and commissioning their production test systems, says: "For the F80, we wanted an audio test system that would allow us to fully customise and automate our production testing. We wanted to design a flexible, hierarchical user interface that could run our entire test sequence automatically, but which could also be manually over-ridden by the operator, in order to run individual tests and adjust settings on demand. This was an important requirement, as this approach allows our experienced test engineers to find and fix problems much more quickly than if they had to wait for the entire test to execute, and then try to interpret pages of results to find the source of the problem."

Enter Prism Sound dScope Series III
For Holmes, there was only one audio test system on the market that could do everything he needed - and that was the Prism Sound dScope Series III audio analyzer.

Also conveniently based in Cambridgeshire, Prism Sound has been manufacturing a range of high quality professional test equipment for audio applications since its inception in 1987. Prism Sound audio test equipment is used by many major consumer electronics brands in automotive, home entertainment, personal mobile, communications and other market sectors as well as most of the world's leading broadcasters including the BBC.

The company's dScope Series III was the ideal choice for Meridian because it offered the ability to customize scripting for the production line.

"The audio test equipment we were using on other products just couldn't handle what I needed it to do," Holmes explains. "I thought the dScope was an ideal solution. It was already being used by our R&D engineers, who have three in their department, so I knew what it was capable of. The importance of the F80 gave us the impetus we needed to make the change."

Prism Sound's dScope Series III is a comprehensive and powerful measurement system for analogue and digital audio generation and analysis, including digital audio carrier analysis, acoustic transducer testing and testing of Windows® sound devices. This industrial strength audio test and measurement system comprises a Windows PC (XP® and Vista® compatible) software application coupled with an external high-precision audio I/O processor for equipment-under-test (EUT) connections.

Production Test Development
Meridian invested in two dScope units and two multi-channel switching units for its production line and once they were delivered, Holmes spent 12 weeks designing the test scripts to suit his exact requirements.

"I must admit I didn't realise Prism Sound could have helped with this, otherwise it might have taken less time," he laughs. "However, once I got to grips with the software it wasn't all that difficult - it was simply a matter of developing the right sequence of tests and applying these to our production line process."

The F80 incorporates three channels of power amplification, AM/FM and DAB receivers (UK model), optical digital output and input, headphone output, two auxiliary inputs and a DVD ROM drive, all of which are fully tested using a Prism Sound dScope Series III analyser in conjunction with a dS-NET I/O switcher. Figure 1 shows the F80 rear panel connections.

To ensure that customers experience only the highest quality audio visual experience, all Meridian products face a rigorous series of tests before leaving the factory. The process starts with flying probe testing of populated PCBS, followed by soak-testing of assembled units, comprehensive audio and video performance /functionality testing and ending with a human audition.

Analysis requirements
Using dScope Series III, the F80's distortion response, frequency response, gain and noise is checked on each output channel for every source input, in addition to checking digital frame rates and channel status information on the digital outputs. Dolby/DTS down-mixing and bass management are also tested using pre-recorded tracks on a DVD test disc, and the F80's dynamic equalisation curves are checked using swept results. Rather than exploit dScope's rapid production testing tools such as multi-tones, Meridian prefer to use slower testing techniques, such as sweeping results, and one channel at a time.

"This slows down the testing to a human level, allowing the operator to see the test results being presented in real time, and allowing the units to warm up to operating temperatures during testing", remarks Holmes. "This also enables us to verify that output devices have been correctly coupled to their heat-sinks, and that thermal limiting circuits are operating at the correct cut-offs."

User interface using Script Dialogue
Holmes has created a custom user interface using dScope Series III's script dialogue controls. The default view of Holmes' test configuration is shown in figure 2. This interface allows the user either to run the complete functional test sequence by selecting the 'Test Go' command, or to select an individual sub-routine from the menu. By clicking on the 'Front Panel - Manual Control' command, the user is able to configure the I/O switcher and to take over control of the dScope - see Figure 3. This flexibility gives the operator the choice between a completely automated, linear test sequence, or alternatively to take over manual control of a smaller sub-set of the test to enable rapid diagnosis of test failures and effective debugging.

Controlling the F80 from dScope
In order to control the F80 during production testing, Holmes has implemented serial port communication from within his dScope Series III automation scripts. This facility allows dScope to address a serial port on the host PC, which in turn is used to control the F80 via its RS232 port. This enables F80 functions such as track selection, volume/EQ settings and input selections to be controlled from dScope's automation scripts. Figure 4 shows Holmes' custom RS232 control interface, which enables the operator to manually over-ride control of the F80 during debug-mode testing.

The dScope Series III audio analyzer has undoubtedly helped Meridian raise the bar with its production line testing for the F80, to the extent that Holmes is now considering purchasing more units so that they can be implemented on the production lines for other Meridian products.

"The units have certainly proved to be a worthwhile investment and the fact that our operators can interact with them is a huge bonus," he says. "I am very impressed with what we have been able to achieve and I can certainly see a role for them in other areas of our production."