Jitter in Digital PA Technology

Understanding and minimising jitter in Audio over IP systems

In modern PA technology, digital signal transmission plays a key role. Systems such as Dante® and Audio over IP (AoIP) revolutionise how audio signals are transmitted over long distances. However, despite great technological developments, jitter still remains a challenge. This article will shed some light on the meaning of jitter, how it emerges in practical application and the effects on audio quality. We are going to show you ways how expert planners and installers can effectively minimise jitter.

What does jitter mean?

Jitter means unwanted variations in the time sequence of digital signals. These variations occur if the intervals between individual data packets of the audio transmission are inconsistent. In audio technology, this simply means that the data packets for transmitting audio signals do not reach their destination at regular intervals.

Such fluctuations result in undesired artefacts such as distortion or crackling noise. Audio over IP systems which transmit audio signals in data packets via networks can particularly suffer a serious loss in sound quality due to jitter.

Causes for jitter

In a network which transmits audio data, jitter may occur due to the following reasons:

Fluctuations in the network connection
Faulty metronomes or
Latency in the network switches

Jitter may also occur if the synchronisation of different devices within a Dante® system is not at an optimum. Clocking is another problem which also often occurs, i.e. the (missing) synchronisation of the devices with a master clock. An increased jitter may occur if the master clock is unstable or if multiple metronomes compete against each other, i.e. a poor reproduction quality because audio signals reach the speakers in the wrong sequence.

Effects on audio quality caused by jitter

The effects on audio quality caused by jitter can vary, depending on the intensity. In less serious cases, the sound quality is only slightly reduced by jitter. This is hardly perceptible to the untrained human ear. With greater fluctuations, clear distortion may appear which can considerably affect your listening experience. With professional PA applications which require a high sound quality, jitter can be the difference between an acceptable and an excellent audio performance.

Use these strategies to minimise jitter

Experts can consider the following strategies to minimise jitter in Audio over IP systems:

Use high-quality metronomes: with a precise and reliable metronome, you will reduce jitter. Please remember that all of the devices in the network are synchronised and use a reliable metronome.
Optimise the network: a well-structured network can minimise jitter. The network should be adapted to audio transmissions. This includes:
1. selection of the right network switches,
2. minimised latencies and
3. as few network overloads as possible.
Apply jitter correction technologies: modern audio devices often provide integrated jitter correction algorithms which can actively compensate jitter. In challenging environments, the application of such technologies can improve the audio quality considerably.

Public address solutions with Dante®

3 applications and tips for installers and expert planners: minimise jitter in audio projects

1. Audio project in a restaurant: focus on synchronous metronomes

In a restaurant, the atmosphere can strongly depend on the quality of background music. In case of jitter, unpleasant sound distortion may occur which can irritate the guests. In order to avoid this, high-quality network switches should be used which are optimised for audio transmission. A central clocking system is mandatory. It ensures that all of the audio devices used in the restaurant are synchronised, e.g. amplifiers, speakers and possible integrated microphones. An example may be the implementation of a Dante® network with a precise metronome which operates as a master clock and thus reduces jitter and provides a pleasant sound experience.

Tip: never use cheap network components which are not specifically designed for audio transmissions. Instead, use devices which are specifically developed to meet the special requirements of Audio over IP applications.

2. Audio project in a shopping centre: optimise the network structure

Shopping centres often apply audio systems to transmit background music, advertisements, announcements and alarm signals. A reliable audio transmission without jitter is particularly important in this area, also with regard to safety. Acoustics in large and open spaces can often be very difficult. Hence, a Dante® network which can be used in multiple audio zones can help to perfectly distribute audio signals. Devices with jitter correction are able to provide a solution to this problem, e.g. available in digital signal processors (DSPs) or Dante-enabled amplifiers.

Tip: When planning the network, ensure a star-shaped topology in which each audio device is directly connected to a central switch. This structure minimises latency and reduces the risk of jitter. Thus, the signals are not transmitted unnecessarily over long distances using multiple junctions.

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3. Audio project in the lecture hall: application of jitter correction technologies

In a lecture hall, an excellent speech intelligibility and a high-quality audio reproduction are essential for presentations. For this purpose, it is important that all of the audio signals from different sources are exactly synchronised, e.g. microphones, laptops or audio playback systems. The application of devices with integrated jitter correction, e.g. modern DSPs can ensure that audio signals are transmitted without distortion, even in more complex transmissions.

Tip: Use a metronome with a low jitter rate in each central audio device which transmits signals in the network. In addition, it is advisable to specify a dedicated master clock device which will be a stable and reliable metronome when setting up a Dante® system.

Jitter is a crucial element of digital PA technology which can considerably affect your audio quality

It is important to understand the origin and effects of jitter. With suitable measures, you can ensure that your audio transmissions are always of the highest quality. No matter whether you choose the right metronome, optimise the network or apply modern correction technologies, there are numerous ways to effectively minimise jitter and to keep the sound quality on a professional level.

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