Switching matrix network for digital audio signals

Details Switching matrix network for digital audio signals Switching matrix network for digital audio signals

1990-03-09

1992-03-24

Yusko, Donald J.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

3408257, 370 581, 375119, H04Q 1104, H04L 2536, H04J 306, H04H 700

Patent

active

050992341

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

3. Field of the Invention
The invention is directed to a switching matrix network for digital audio signals that are supplied to the inputs of the switching matrix network in parallel representation via incoming data busses in individual sampling clock sequences having sampling frequencies that deviate from one another and are transmitted in identical parallel representation to identical, outgoing data busses via arbitrarily switchable outputs of the switching matrix network, whereby a suitable switching matrix network sampling clock is provided for the switching events within the switching matrix network.
2. Description of the Related Art
It can occur in switching equipment for digitized audio signals in the sound recording studio field that the PCM signals at the inputs of the switching matrix network have different sampling rates. This particularly leads to problems when the couplers had a fixed sampling rate prescribed for them. In systems having a great number of channels, it seems beneficial to use the same coupler for all channels, since, thus, the hardware outlay for the actual switching matrix network can be kept low in comparison to a plurality of sub-couplers having differing "switching rates". The object thus arises to exactly maintain the sampling rate when coupling pulse-code-modulated signals, i.e. that the individual sampling frequency with which a signal is supplied to the input of the switching matrix network should also be preserved in the signal taken from the respectively coupled output. If, namely, the sampling rates were to vary within shorter time intervals, then this would involve a deterioration of the quality of the signal reconstructed after the digital-to-analog conversion.
U.S. Pat. No. 3,868,481 discloses a time-division multiplex through-connect system (switching matrix network) for digital signals that works with different bit rates that derive due to different word lengths (6 or 8 bits per byte) and different combinations of channels (or words) of 6, 12 or 24 channels per frame. In this system, however, the sampling rate for all channels is the same, this, of course, being a prerequisite for these channels to be capable of being combined to form a higher-ranking channel (highway). The incoming signals are converted by input units to a uniform byte and frame format that is then offered to the switching matrix network.
The sampling rate of the outgoing signals is synchronous with the coupler clock multiplied by a rational factor. This must be appropriately selected in order to be able to switch the total of signals sampled with, for example, 8 kHz. A periodic data loss that is compensated by resetting buffer memories (elastic buffers) arises due to slight frequency differences. The system disclosed by the U.S. Patent is not suitable for signals having input sampling frequencies that deviate greatly from one another, as is possible in the switching matrix network of the invention.


SUMMARY OF THE INVENTION

The object of the invention is to produce the switching of audio signals with different sampling rates with the assistance of a single switching matrix network having minimum outlay. This is inventively achieved in that, for the purpose of achieving a coincidence of the sampling clock sequences at the outputs of the switching matrix network and those at the respectively allocated inputs of the switching matrix network, the switching matrix network sampling clock has a sampling frequency that is greater than all individual sampling frequencies, and in that, first, a respective input intermediate memory chain is provided at the switching matrix network inputs and has a respective, allocated clock comparison circuit for acquiring a respective interference signal that is a measure for the phase difference or, respectively, frequency difference between the individual sampling frequency and the sampling frequency of the switching matrix network, whereby the interference signals are transmitted in coded form during the sampling periods of the switchi

REFERENCES:
patent: 3868481 (1975-02-01), Patrusky et al.
patent: 4639910 (1987-01-01), Toegel et al.
patent: 4808008 (1989-02-01), Guerillot
patent: 4841548 (1989-06-01), Volejnik
patent: 4894821 (1990-01-01), Hayano

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