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Alle die mit uns auf Kaperfahrt fahren, müssen Männer mit Bärten sein. Jan und Hein und Klaas und Pit, die haben Bärte, die haben Bärte. Jan und Hein und Klaas und Pit, die haben Bärte, die fahren mit.

  • Sennheiser AVX - Digital Wireless Microphone System for Audio for Video
    https://www.proaudio.de/en/specials/16714-sennheiser-avx.html

    Author and Photos: Peter Kaminski - At the NAB show in April 2015, Sennheiser unveiled its AVX digital wireless audio system for video cameras. The system differs in many points from previous wireless microphone systems used for audio for video. There is plenty for us to report about.
    DECT

    The first new feature is the transmission format and frequency range. This is a vitally important point in the wake of restrictions regarding frequency allocations for wireless microphone systems. The AVX developers decided against using the UHF frequency range or the LTE gap and opted instead for DECT. Initially, DECT stood for Digital European Cordless Telephony. The aim was to introduce a modern standard for wireless telephony. However, it soon became clear that the system offers more potential than just for wireless telephones. Today, DECT therefore stands for Digital Enhanced Cordless Telecommunications. In the meantime, DECT is used for industrial communication and for intercom systems on stage, as well as for remote-controlled systems, for example in the form of remote-controlled power sockets, etc.

    DECT was defined as a standard by ETIS (European Telecommunications Standards Institute). In 1992, DECT was subsequently introduced and a frequency range was also specified for this application throughout Europe. CEPT recommended that telecommunications authorities should not demand any fees or licences for using DECT. As a result, DECT can be used throughout Europe free of charge.

    The frequency range in Europe is 1880 to 1900MHz, in other words a 20MHz segment. However, DECT has also become established beyond Europe’s borders. For example, DECT can also be used in the same frequency range in India, Indonesia, Hong Kong, Singapore, Malaysia and Australia. In North and South America however, the frequency range for DECT is 1,920 to 1,930MHz (with the exception of Brazil, where it is 1,910 to 1,920 MHz). In Japan it is 1,893 to 1,906MHz and in Taiwan 1,880 to 1,895MHz.

    DECT also includes dynamic frequency allocation. This means that users need not worry about selecting the right operating frequency, as this is done by the end device itself. If interference is detected on one channel, the frequency is automatically changed. Transmission is bidirectional, in other words in both directions, although the data transfer rate can differ in the two directions. DECT provides 24 time slots in a 10-millisecond frame, and these can be used as required for either direction (up and down stream). DECT portable devices can be connected via a base station, something which we are familiar with from cordless phones, but a point-to-point connection is also possible. The maximum allowed power is 250mW.
    Concept and Technology

    But let’s now return to Sennheiser’s AVX system. The requirements to be met by high-quality audio transmission are, of course, significantly higher than for the audio bandwidth of a DECT telephone, which is limited to 7 kHz. This is achieved by a number of measures: firstly by the above-mentioned asymmetry of the data rates (the return path requires less bandwidth than the main path in an application), by bundling several channels and by using audio coding with data compression. In AVX, the three-fold channel width of a normal DECT channel is used.

    As a result, the system offers an audio transmission range of 20Hz to 20kHz with a sampling rate of 48kHz and a resolution/word width of 24bits. A signal-to-noise ratio of over 90dB (A-weighted) is achieved. Instead of the 64-bit or 128-bit encryption usually used for DECT, AVX uses tap-proof 256-bit AES encryption.

    The latency of the AVX system is 19 milliseconds and is essentially determined by the audio codec. The codec is a speech-optimised codec based on the CELT codec. It was specially adapted and optimised to Sennheiser’s requirements. CELT (Constrained Energy Lapped Transformation) is itself based on the speech-optimised CELP codec (Code-Excited Linear Prediction), which was developed for very low data rates. Unlike CELP, CELT works exclusively on the frequency domain and, in spite of being optimised for speech, it supports both speech and music.


    ...
    Sven Boetcher: A charging station is not planned, because we wanted to make everything as simple and as transportable as possible. For that reason, the accupack has a USB charging socket which works with every USB charging cable, every power bank and every mobile phone charger. It couldn’t be easier than that.

    #DECT #microphone #wireless #broadcast