# US 5,706,335 A · Method and appartus for transmitting coded audio signals through a transmission channel with limited bandwidth > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,706,335 A - Document ID: US5706335A - Status: Granted - Kind: A - Application number: 08/419,199 - Filed: 1995-04-10 - Granted: 1998-01-06 - Earliest claimed: 1995-04-10 - Assignees: Corporate Computer Systems - Inventors: Larry Hinderks - Web page: https://patentgrep.com/patent/US5706335A ## CPC - H04Q 11/0421: {Circuit arrangements therefor} - H04R 1/005: {using digitally weighted transducing elements} - H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract A digital audio transmitter system capable of transmitting high quality, wideband speech over a transmission channel with a limited bandwidth such as a traditional telephone line. The digital audio transmitter system includes a coder for coding an input audio signal to a digital signal having a transmission rate that does not exceed the maximum allowable transmission rate for traditional telephone lines and a decoder for decoding the digital signal to provide an output audio signal with an audio bandwidth of wideband speech. A coder and a decoder may be provided in a single device to allow two-way communication between multiple devices. ## Claims ### Claim 1 A portable CODEC for transmitting high quality audio signals over a standard telephone line having a limited bandwidth and a maximum transmission rate, said portable CODEC comprising: a single portable housing; an analog mixer, within the housing, receiving an input audio signal from at least one input line, said audio mixer amplifying and mixing input audio signals to produce a single combined audio input signal; memory, within the housing, storing a lossy compression routine and storing at least one set of predefined psycho-acoustic parameter levels for said compression routine; an encoder, within the housing, converting said single combined audio input signal to a combined digital input signal at a predefined sampling rate and encoding said combined digital input signal based on said lossy compression routine stored in memory to produce a single encoded digital signal having a predefined compression ratio with respect to said single combined audio input signal; an analog modem, with the housing, establishing a connection with, and a transmission rate for, a standard telephone line of a telephone network, said modem converting said encoded digital signal to an encoded analog output signal and outputting said encoded analog output signal at said transmission rate established by said analog modem along the standard telephone line through the telephone network; and a control processor, within the housing, defines said predefined sampling rate for said encoder based on said transmission rate established by said analog modem to enable said analog modem to output said encoded analog output signal at a transmission rate that does not exceed the maximum transmission rate of the telephone line. ### Claim 2 (depends on 1) A portable CODEC according to claim 1, further comprising a clock generator providing synchronous clock signals to said encoder and analog modem. ### Claim 3 (depends on 1) A portable CODEC according to claim 1, wherein said controller defines said sampling rate to equal approximately one-half of said transmission rate established by said analog modem. ### Claim 4 (depends on 1) A portable CODEC according to claim 1, further comprising: a microphone connected to a microphone input line, said microphone input line receiving live, real time analog audio signals. ### Claim 5 (depends on 1) A portable CODEC according to claim 1, further comprising: an input line adapted to receive an analog audio signal from an audio playback device. ### Claim 6 (depends on 1) A portable CODEC according to claim 1, further comprising means for adjusting a voltage level of input audio signals on said at least one input line. ### Claim 7 (depends on 1) A portable CODEC according to claim 1, wherein said analog mixer receives, amplifies and mixes at least two input audio signals to produce said single combined audio input signal. ### Claim 8 (depends on 1) A portable CODEC according to claim 1, further comprising audio level LEDs connected to said audio mixer indicating when a voltage level of said single combined audio input signal exceeds a threshold level. ### Claim 9 (depends on 1) A portable CODEC according to claim 1, wherein said analog mixer comprises: line amplifiers amplifying input audio signals on at least two input lines; line level controllers, connected to said amplifiers, adjustable by a user, said level controllers controlling an output voltage to which input audio signals are amplified by said amplifiers; and an input mixer mixing amplified audio signals output by said level controllers to produce said single combined audio input signal. ### Claim 10 (depends on 1) A portable CODEC according to claim 1, wherein said analog mixer comprises: normal and overload signal detectors comparing said single combined audio input signal with normal and clip thresholds defining normal and overload volume levels, respectively; and normal and overload LEDs connected to said normal and overload signal detectors, respectively, said normal LED lighting when said single combined audio input signal is at said normal threshold, said overload LED lighting when said single combined audio input signal is at said overload threshold. ### Claim 11 (depends on 1) A portable CODEC according to claim 1, wherein said encoder encodes said combined digital input signal based on predefined psycho-acoustic parameter levels stored in memory that produce encoded digital signals having a bandwidth range of approximately 20 Hz to 5,500 Hz. ### Claim 12 (depends on 1) A portable CODEC according to claim 1, wherein said encoder encodes said combined digital input signal based on predefined psycho-acoustic parameter levels stored in memory that produce encoded digital signals having a bandwidth range of approximately 300 Hz to 3,000 Hz. ### Claim 13 (depends on 1) A portable CODEC according to claim 1, wherein said encoder encodes said combined digital input signal based on an ISO/MPEG layer II compression routine having predefined psycho-acoustic parameter levels that produce an encoded digital signal having a bandwidth range of approximately 20 Hz to 5,500 Hz. ### Claim 14 (depends on 1) A portable CODEC according to claim 1, further comprising: an error protection processor adding error protection data to said single encoded digital signal based on a predefined error protection format to produce an encoded and error protected digital signal, said analog modem outputting said encoded and error protected digital signal as said output signal. ### Claim 15 (depends on 14) A portable CODEC according to claim 14, wherein said predefined error protection format is a Reed-Solomon error protection format, said error protection processor providing both burst and random error protection. ### Claim 16 (depends on 1) A portable CODEC according to claim 1, wherein said analog modem receives a single incoming encoded analog signal from said standard telephone line on said telephone network, said modem converting said single incoming encoded analog signal to a single incoming encoded digital signal. ### Claim 17 (depends on 16) A portable CODEC according to claim 16, wherein said incoming encoded analog signal contains error protection data, said CODEC further comprising: an error correction processor performing error correction upon said incoming encoded digital signal based on said error protection data to produce an incoming error corrected encoded digital signal. ### Claim 18 (depends on 17) A portable CODEC according to claim 17, wherein said error correction processor comprises: an error correction encoding circuit generating parity information based on said incoming encoded digital signal; and a Reed-Solomon encoder receiving and preparing corrupted data bits in said incoming encoded digital signal based on said parity information to correct errors produced during transmission through the telephone network. ### Claim 19 (depends on 18) A portable CODEC according to claim 18, wherein a code of said Reed-Solomon encoder includes code blocks containing approximately 178-bit data words and 8-bit parity words. ### Claim 20 (depends on 16) A portable CODEC according to claim 16, further comprising: a decoder decoding said incoming encoded digital signal from said analog modem based on a lossy decompression routine stored in memory to provide an analog output signal. ### Claim 21 (depends on 20) A portable CODEC according to claim 20, wherein said control processor is selectable by a user between multiple modes of operation, said control processor, when in a test mode, bypassing said telephone network and directing said single encoded digital signal from said encoder directly to said decoder to allow testing of said compression and decompression routines stored in memory. ### Claim 22 (depends on 20) A portable CODEC according to claim 20, further comprising a clock generator for providing synchronized clock signals to said encoder and decoder. ### Claim 23 (depends on 20) A portable CODEC according to claim 20, wherein said decoder comprises: memory storing an ISO/MPEG decompression routine; and a digital single processor decoding and converting said incoming encoded digital signal based on said ISO/MPEG decompression routine stored in memory to produce said analog output signal. ### Claim 24 (depends on 23) A portable CODEC according to claim 23, wherein said decoder further comprises: a D/A converter converting a digital output of said digital signal processor to said analog telephone signal. ### Claim 25 (depends on 24) A portable CODEC according to claim 24, wherein said decoder further comprises a D/A clock generation unit generating synchronous timing signals for said D/A converter and digital signal processor. ### Claim 26 (depends on 1) A portable CODEC according to claim 1, further comprising: a headphone amplifier outputting said analog output signal to a headphone output line; and a volume control controlling a volume of said analog output signal at said telephone output line. ### Claim 27 (depends on 26) A portable CODEC according to claim 26, wherein said headphone amplifier further comprises: record and local monitor level controls receiving and adjusting levels of said single combined audio input signal from said analog mixer and of said analog output signal from said decoder, respectively; and a headphone mixer amplifier mixing output signals of said record and local monitored level controls to output a mixed record/local output signal at said headphone output line. ### Claim 28 (depends on 26) A portable CODEC according to claim 26, wherein said headphone amplifier further comprises: a record mix controller operative by the user, receiving said combined audio signal from said analog mixer, said mix controller controlling a level of said combined audio input signal; and a record output amplifier controlled by said record mix controller outputting said combined audio input signal at a desired level to a record output. ### Claim 29 (depends on 1) A portable CODEC according to claim 1, wherein said control processor comprises: a keypad/LCD interface adapted to communicate with a keypad and LCD display respectively; and a microprocessor communicating with the user through the keypad/LCD interface. ### Claim 30 (depends on 1) A portable CODEC according to claim 1, further comprising: a keypad entering input commands to said control processor; and a LCD display displaying responses to said input commands and displaying alert messages. ### Claim 31 (depends on 30) A portable CODEC according to claim 30, further comprising: a programmable interval timer circuit interfacing said control processor with said keypad and LCD display. ### Claim 32 (depends on 31) A portable CODEC according to claim 31, further comprising: a universal asynchronous receiver/transmitter providing a synchronous input/output data to said control processor from an external computer through a rear panel remote control port and rear RS 232 port in said receiver/transmitter. ### Claim 33 (depends on 1) A portable CODEC according to claim 1, wherein said encoder comprises: an A/D converter converting said combined audio input signal to a digital pulse code modulated signal at said predefined sampling rate; and a digital signal processor encoding said digital pulse code modulated signal based on a modified ISO/MPEG compression routine stored in said memory to produce said encoded signal. ### Claim 34 (depends on 33) A portable CODEC according to claim 33, further comprising: an A/D clock generation unit generating timing signals for said A/D converter and digital signal processor based on said transmission rate established by said analog modem.