摘要:
The present invention discloses a system and a method for transmitting DTMF signals over high speed digital networks using voice compression algorithms, and particularly to a system for ensuring the integrity of DTMF signals at the destination node of a network after compression and decompression of data on a voice connection. A DTMF Detector is placed in parallel with a voice compression unit performing the compression algorithm. When a candidate DTMF signal is detected, the signal component at the higher frequency in the candidate is filtered out to eliminate the possibility of double DTMF detection at end user equipment. When the candidate DTMF signal is finally validated by the source node as representing a true DTMF signal, only the data essential for reconstituting the DTMF signal are transferred to the destination node.
摘要:
A method for detecting the presence of voice, single tone and dual tone signals compares a ratio r which equals the square of the maximum value of the received signal (A max) during a sampling period divided by a measure E of the energy to three different thresholds. If r is less than the first threshold (3), a single tone is indicated. If it is greater than the first but less than the second, the received signal level is compared to the third threshold (-43 dB) and receipt of a voice signal is indicted if the level of the received signal exceeds this threshold.
摘要:
A method for detecting the presence of voice, single tone and dual tone signals compares a ratio r which equals the square of the maximum value of the received signal (A max) during a sampling period divided by a measure E of the energy to three different thresholds. If r is less than the first threshold (3) a single tone is indicated. If it is greater than the first but less than the second (5.2) a dual tone is indicated. If it is greater than the second, the received signal level is compared to the third threshold (-43 dB) and receipt of a voice signal is indicated if the level of the received signal exceeds this threshold.
摘要:
A method for detecting the presence of single tone and dual tone signals compares a ratio r which equals the square of the maximum value of the received signal (A max) during a sampling period divided by a measure E of the energy to three different thresholds. If r is less than the first threshold (3) a single tone is indicated. If it is greater than the first but less than the second (5.2) a dual tone is indicated. When a single tone is indicated the received signal is subjected to a second order autoregressive process to determine the frequency of the single tone. If a dual tone is indicated the received signal is subjected to a fourth order autoregressive process to determine the frequencies of the dual tones.
摘要:
A Decimation filter for converting a train of sigma-delta pulses S(i) in synchronism with a sigma-delta clock (fs) into a train of Pulse Coded Modulation (PCM) samples in accordance with the formula ##EQU1## where Cn is the sequence of the coefficients of the decimation filter which corresponds to a determined decimation factor, and the PCM samples being processed by a Digital Signal Processor (DSP). The decimation filter includes a device for storing a digital value representative of the DC component introduced during the sigma-delta coding process, with the digital value being computing by the DSP processor during an initialization phase. The decimation filter further includes a device operating after the latter initialization phase for subtracting the stored digital value from each of the PCM samples so that the resulting sequence of PCM samples appears free of any DC component introduced during the sigma-delta coding. This accurate DC component suppression is achieved without necessitating the use of additional digital signal processor resources from the processor. Preferably, the decimation filter comprises a device for detecting a saturation occurring in the computing of the PCM sample, and responsive to the saturation detection, for transmitting a predetermined PCM sample to the DSP processor.
摘要:
An adaptive apparatus and method for managing a playout buffer (POB) in an edge node of a packet-based data communications network, such as an ATM network, in order to reduce the end-to-end communication delay introduced thereby and to allow the POB filling level to be corrected in the event of clock speed differences. A monitoring mechanism determines if the minimum filling level of the playout buffer over a time period whereby the average filling level of the playout buffer is reduced according to the minimum filling level of the playout buffer over the time period.
摘要:
A processing unit for performing convolution computation according to the HARVARD architecture which includes a first and second input register for receiving a first and second operand, a multiplier for multiplying the operand and a Arithmetic and Logic Unit (ALU) circuit. The unit further includes a coefficient storage memory which is used for loading at least one set of coefficients allowing the convolution computation. The memory storage is addressed either from an internal address generator or directly from the internal data bus thereby allowing the possibility to store either coefficients or data into the memory. The flexibility is still increased by the use of a particular set of multiplexing circuits allowing multiple configurations. An internal address generation circuit is used for performing a partial addressing of the set of coefficients thereby providing decimation capability.
摘要:
A decimation filter for converting a train of sigma-delta pulses S(i) in synchronism with a sigma-delta clock (fs) into a train of PCM samples which includes counters (321, 331, 341) driven by the sigma-delta clock (fs) and which is continuously incremented by one during N sigma-delta clock pulses, then decremented by two during N following sigma-delta clock pulses and then incremented again by one during N following sigma-delta clock pulses in order to provide a sequence of incrementation parameter DELTA(n). The decimation filter further includes storages (320, 330, 340) for storing the value of the coefficient C(n) corresponding to the decimation filter transfer function, and incrementers (327, 337, 347) driven by the sigma-delta clock fs for incrementing the storages with the incrementation parameter DELTA(n). Finally, the decimation filter includes computers (323, 333, 343, 327, 337, 347) for deriving from the contents C(n) of said storages and from the train of input sigma-delta samples S(i+n) one Pulse Code Modulation (PCM) sample every 3.times.N input sigma-delta samples according to the formula: ##EQU1##
摘要:
Process for transmitting compressed voice circuits over a packet switching network of the type comprising a plurality of switching nodes (SW-1 to SW-7) interconnected by connection lines and including at least an end switching node (SW-1) connected to a source exchange telephone device (PABX A) and another end switching node (SW-3) connected to a destination exchange telephone device (CX), and comprising the steps of receiving from the source exchange telephone device a sequence of uncompressed frames wherein each frame contains n slots containing each J bytes respectively associated to J voice circuits, compressing the data bits of each voice circuit in order to build a packet containing J compressed voice circuits, and providing this packet to the end switching node for transmission to the destination exchange telephone device.
摘要:
Repetitive packets in a voice/data stream, are detected and suppressed in the transmitting side of a network, after a predefined number of consecutive repetitive packets have been transmitted. Then, at the receiving side of the network, suppressed repetitive packets are reconstituted by filling the resulting gap in the voice/data stream with the repetitive pattern contained in the last received repetitive packet. When the input voice/data stream is compressed, only non-repetitive packets are compressed so that repetitive patterns are not corrupted by compression.