To deliver quality sound, it is essential to analyze the sound produced and captured during R&D. A multitude of parameters are critical to authentic sound reproduction
New electroacoustic devices such as mobile phones, tablets, and speakers, keep pushing the boundaries of design. The latest smartphone must squeeze in ever-more impressive capabilities to compete in a crowded market, and fulfill international telephone standards for voice capture and reproduction. And whether customers want open-backed headphones or flat frequency response speakers, manufacturers need to deliver the quality of sound that buyers expect, as promised by the brand.
Engineering quality sound reproduction
To deliver quality sound, it is essential to analyze the sound produced and captured during R & D. A multitude of parameters are critical to authentic sound reproduction. These include distortion, frequency response, and directivity. Since finding the right balance can require many tests, automation, data correlation, and ease of use help ensure productive electroacoustic testing.
Simulating real-life phone use
Behind the scenes of a simple telephone call, a multitude of processes are at work to make it effortless. To eliminate background noise while isolating the caller’s voice – even while the phone is on a table – smartphones use multiple microphones and sophisticated algorithms. Testing capabilities like these require precision measurement equipment. And most test parameters demand versatile analysis systems with sophisticated data management.
Telephone standards testing
Modern communication devices, smartphones and Voice over Internet Protocol (VoIP) terminals must meet many national and international regulations, plus those set by network operators. This enables equipment to communicate efficiently with similar devices around the world. The regulations define their minimum performance quality abilities, such as the speed at which they switch between speaking and receiving, and their speech intelligibility. The methods used to test these parameters are laid out in great detail in a multitude of standards – which our software incorporates and guides users through to ensure that nothing is overlooked. These standards include ITU-T, ETSI, 3GPP, etc.
The acoustic performance of telephones, whether they are mobile devices or corded phones, is key to both end-user acceptance and compliance with international and national standards. Users demand high voice-quality in all situations, so the acoustic perception of a device is critical. Acoustic performance is particularly significant for mobile phones, where conversations can take place almost anywhere, from a quiet office to a noisy street or a busy call centre.
Both corded and cell phones alike need advanced acoustic and electronic signal processing combined with superior design and compact size. The strict testing regimes go right through the development and production processes of telephones. With every design change in a phone, R&D needs to assess the impact on the acoustic performance. Finished designs must go through voice testing to ensure quality and intelligibility and live up to national and international standards, including 3GPP TS.26.132, 3GPP2 C.S0056, YD/T 1538, CES-Q003-2, CMCC, ITU-T P.862 (PESQ) and ITU-T P.863 (POLQA). Once in production, quality assurance, sample testing and validation are conducted on an ongoing basis and all components go through rigorous incoming inspection.
Using a Brüel & Kjær Head and Torso Simulator (HATS) with ear and mouth simulators connected to our telephone testing software, it is possible to evaluate headsets and handsets in situ on a range of acoustic performance parameters. Parameters include signal reception and transmission, acoustic side tones and background noise characteristics, giving you realistic measurements of the telephone performance.
When evaluating the acoustic performance of hands-free communication devices such as in-vehicle audio and communication systems, conference phones, or laptop VoIP technologies, it is important to take into consideration the surroundings, as well as the acoustic influence of the head and body. In addition to traditional parameters for characterization of communication devices, such as frequency response, loudness rating and directivity response, it is necessary to determine transmission quality in the presence of background noise, switching, and echo cancelling, as these are known to have close correlation with the audio performance and perceived quality of the reproduction of the human voice of hands-free equipment.
For testing hands-free devices, we suggest a system that simulates real life communication situations as closely as possible, without letting the physical presence of a human interfere with the measurements. The system consists of a HATS with ear and mouth simulators, a measurement front end and the PULSE-based Voice Testing Software for Hands-free-equipment Type 7909-NS1. The software has capabilities for both data acquisition and data analysis, according to standards set by VDA (Verband der Automobilindustrie). This configuration can be used both in a lab setting and for in-vehicle testing of audio performance.
Since the introduction of the Sony Walkman® in the late 1970s, portable devices with audio capabilities and head- or earphones have become commonplace. Consumers have high expectations for the acoustic performance of head- and earphones. These have to deliver great audio quality while striving to protect the listener’s hearing. When developing and testing headphones, the influence of the pinnae (the outer portion of the ear) should be taken into account and a realistic acoustic loading simulated, so realistic evaluations of open, closed and insert headphones can be made.
Type 4128-C is a head and torso simulator with built-in ear simulators that provides a realistic reproduction of the acoustic properties of an average adult human head and torso. When used with an input-output LAN-XI module and our PULSE-based Electroacoustic Testing Software Type 7797, it enables you to determine a variety of headphone characteristics in situ. Characteristics include:
- Output response
- Frequency response
- Harmonic distortion
- Acoustic loading
- Simulated insertion responses
- Left/right tracking
- Background noise insertion loss
The system can be configured to support EN 50332, a European standard on the maximum sound pressure level permitted from portable audio players.
Hearing aid designers have to take into consideration a long list of expectations and corresponding challenges, including:
- Improving speech intelligibility in noise
- Reproducing nature’s sounds
- Making soft sounds audible
- Ensuring that loud sounds are never uncomfortably loud
- Ensuring optimum music reproduction
- Improving the users’ perception of their own voices
- Optimizing sound reproduction for both in-ear and behind-the-ear hearing aids
When developing hearing aids, you need systems that allow you to test, benchmark, control quality and augment product designs, while taking into consideration quality hearing reproduction and problem-free communication. Systems need to support both traditional, standardized electroacoustic measurements and open and flexible processes that assist in the development of new hearing aid technologies and features.
Typical measurement set-up for hearing aid testing uses an ear simulator (coupler) and an anechoic test box. An anechoic test box provides excellent insulation from external noise, even at low frequencies, and well-defined, uniform test conditions, which are important requirements for obtaining accurate and repeatable measurements for key measurements such as input/output characteristics, internal noise generation and leakage detection. In turn, the coupler allows for easy mounting of and accurate measurements on a wide range of hearing aids. The measurements are managed and data analyzed in our PULSE Electroacoustic Testing Software Type 7907.
Loudspeakers and entertainment systems can be found just about everywhere: phones, cars, TVs, headphones, computers, toys, public announcement systems, and cinemas – the list just goes on. The end user has strong and clear ideas of the performance expected from a product, so it is crucial to transform these expectations into products that satisfy customers. Sound quality measurements help to ensure that customer preferences are met and provide a way to differentiate the product. However, sound quality is not the only parameter a manufacturer may want or need to evaluate:
- Target setting – Are response, distortion, impedance, sensitivity, directivity, and other values where they need to be?
- Acoustic material – How do lighter, more durable and less expensive materials affect the sound?
- Structure – How does a change in cabinet or component design affect the vibrational and acoustic properties of a speaker?
- Production – Can a manufacturer rely on pass/fail results and receive a quality product?
The number of tests involved in the verification of performance specifications and requirements can be overwhelming for an R&D engineer with a deadline and budget to meet. That is why in the industry, standardization, automation, data correlation and ease of use are such hot topics in R&D testing. Providing these features without compromising reliability and precision, means engineers can meet their targets quickly and efficiently.
For loudspeaker testing we recommend PULSE Loudspeaker Test Application BZ-5603. This software supports measurements on loudspeakers, using an instrumentation set-up that includes a turntable to automatically record the directional characteristics of the test object. This application automates measurements of frequency response, harmonic distortion, directional response and calculation of Thiele-Small parameters using the simple impedance, added volume, added mass or laser methods.