Sound quality and the importance of networks

Image explanation: The higher the audio bandwidth and the lower the data compression, the better the conditions for good sound quality.

A young person is able to perceive sounds at frequencies between 20 and 20,000 Hz (20 Hz–20 kHz). This ability changes as we get older and because of other physical factors. An adult is normally able to distinguish sounds at frequencies between 20 Hz and 12 kHz. People used to talk about the concept of 'telephone quality', where, owing to technical limitations, the audio bandwidth only ranges from 200 Hz to 3.4 kHz (i.e. a total of 3.2 kHz). With an analogue telephone system this means losing a large part of the speech content, meaning the sound becomes less natural and more difficult to make out than if the audio bandwidth had been higher. Compare this with FM radio which has an audio bandwidth of up to 15 kHz, enabling both voices and music to be reproduced much more naturally.

* VoIP = Voice over IP, i.e. digital telephony via the data network.

The term ’bandwidth’ insofar as data is concerned refers to the amount of information that can be
transferred per second in a network. Audio bandwidth refers to the sound frequencies (the range
of sounds) that can be transmitted. The use of the term ’bandwidth’ for both these concepts can
sometimes lead to misunderstandings.

Analogue telephony is severely limited in terms of range of sound (approx. 3.2 kHz). Unlike digital
networks, however, the sound signal is not compressed in an analogue network, which means that
the signal remains the same throughout. The analogue signal is perceived by some as ’cleaner’ and
’softer’, even though a digital signal generally tends to contain more units of sound information.
This is because the human ear is extremely good at perceiving changes in the actual sound.

In mobile networks the sound signal is always more or less compressed. Elements of the sound which we cannot perceive are simply removed in order to reduce as much as possible the amount of space taken up by the signal on the network. Advances in technology are helping to increase the capacity of mobile networks and thus also the ability to distribute good sound using less compression. Sound is currently distributed at about 3.2 kHz in the various mobile networks. Sound is most compressed in 2G networks, then slightly less for 3G and significantly less for 4G.
Poor transmitting and receiving conditions also have an impact on sound quality. In the event of poor conditions, the system automatically reduces the size of the information in the network to try to maintain contact. This has a deleterious effect on sound quality (i.e. compression increases) despite the fact that sound is always given priority in transmissions (over images, for instance).

Telephony over a data network is called VoIP (Voice over IP). As the sound produced by old analogue technology has traditionally been acceptable with an audio bandwidth of 3.2 kHz (telephone quality), the sound produced by digital networks was designed to deliver roughly the same sound quality. This was a necessity in the early digital networks, as back then data bandwidth was clearly limited.
There is no specific technical limitation for sound quality in digital networks but this is determined primarily by the chosen codec. A codec is a function in the telephone that converts sound into data and vice versa. The sound from the transmitting telephone is converted to data packages using a codec, whereupon the data packages are sent to the receiving telephone where they are converted back to sound by a corresponding codec. The telephones normally try to transmit sound using the best possible common codec. Modern telephones, which support broadband codecs, tend therefore to be better able to achieve the best possible sound. The last decade has seen incredible advances in the capacity of VoIP.
Common designations for various codecs are: Wideband codec (7 kHz); Super Wideband codec (14 kHz) and Full Bandwidth codec (20 kHz).

A network’s distribution capacity to the office is naturally fundamental to ensuring good sound quality. It is also important to remember that additional wireless solutions added outside the telephony network can interrupt the chain and reduce the capacity of the audio bandwidth. These issues can be caused by wireless systems, such as DECT and Bluetooth®, or even old network products.

Bluetooth® is a standard that was originally developed to enable various accessories to connect wirelessly to a mobile phone or PC. BT only works over short distances between a mobile phone and accessories. There is additional data compression of the sound signal, leading to a deterioration in the sound quality.

DECT solutions for wireless telephony in offices and industrial premises were originally developed for use with analogue telephony. Regardless of the capacity up to the DECT transmitter, it is not possible to produce anything more than normal telephone-quality sound, i.e. 3.2 kHz, in a DECT network. If using a Wideband codec (7 kHz) in a VoIP network, you lose more than 3 kHz for all calls transmitted via the DECT system. This hardly matters for normal telephone calls, but if you are using such a combination and want to hold meetings where sound quality is particularly important, it may be a good idea to use direct connections (cables) to the VoIP network.

Put simply, CAT-iQ is a digital enhancement of DECT. A CAT-iQ system uses a 7 kHz audio bandwidth and thus offers excellent capacity for wireless connections to a VoIP system.

Konftel’s products always deliver optimum sound quality in relation to network capacity. This brief review of sound distribution shows that there are grounds for analysing activities and the organisation before choosing a network and updating your telephony and data infrastructure. Clearly, a VoIP network with Wideband codec (7 kHz), for example, is better equipped to deliver good sound every time than a mobile or analogue network. On the other hand, mobility can be an important consideration in many contexts.
A number of Konftel’s products offer more than one connection option, giving you the opportunity to choose between practical applications (e.g. mobile) and optimum sound quality (VoIP). For instance, the wireless Konftel 300W with its analogue DECT connection can transmit a 3.2 kHz audio bandwidth, while the USB connection for a computer is compatible with a Wideband codec (7 kHz). It is also possible to connect this unit to a mobile phone using a cable.
Irrespective of your chosen solution, there are products in Konftel’s range which simplify and improve opportunities for both rapidly improvised teleconferences at your desk and large meetings in conference rooms and so on. Please contact one of our resellers for more information.