Method and apparatus for transmitting coded audio signals through a transmission channel with limited bandwidth

• US 6,700,958 B2
• Filed: 07/03/2001
• Issued: 03/02/2004
• Est. Priority Date: 04/10/1995
• Status: Expired due to Fees

• Current Assignee: Megawave Audio LLC (Intellectual Ventures LLC)
• Original Assignee: Starguide Digital Networks Incorporated (Extreme Reach, Inc.)
• Inventors: Hinderks, Larry
• Primary Examiner(s): WOO, STELLA L
• Application Number:
  US09/897,250
• Publication Number:
  US 20010038686A1
• Time in Patent Office: 973 Days
• Field of Search: 379/93.31, 379/93.28, 379/93.01, 379/93.05, 379/93.08, 379/399.02, 379/419, 375/222
• US Class Current: 379/93.31
• CPC Class Codes: H04Q 11/0421 Circuit arrangements therefor
• CPC Class Codes: H04R 1/005 using digitally weighted transducing elements

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

1. An portable audio transmission system comprising:

a coder for coding an entire input audio signal into a digital signal in a single encoding process at a transmission speed including 28.8 kbit/s to be transmitted through a traditional analog copper telephone line generally supporting a digital signal transmission rate of at least 28.8 kbit/s; and

a decoder for decoding the digital signal that is received from a telephone network to provide an output audio signal with a frequency range of greater than 4 kilohertz.

2. A portable CODEC for transmitting high quality audio signals over a standard telephone line having a limited bandwidth and maximum transmission rate, said portable CODEC comprising:

a single portable housing;

a memory within the housing and storing a lossy audio compression routine;

an encoder within the housing and including a program to convert an entire audio input signal to a digital input signal in a single encoding process at a sampling rate and encode said digital input signal based on said lossy compression routine stored in memory to produce an encoded digital signal having a compression ratio with respect to said audio input signal;

an analog modem within the housing and 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 processor within the housing and enabling said analog modem to output said encoded analog output signal at a transmission rate that does not exceed a predetermined transmission rate of the standard telephone line, said standard telephone line generally supporting a transmission rate of at least 28.8 kbit/s.

3. A portable CODEC according to claim 2, further comprising a clock generator providing synchronous clock signals to said encoder and analog modem.

4. A portable CODEC according to claim 2, wherein said processor defines said sampling rate to equal approximately one-half of said transmission rate established by said analog modem.

5. A portable CODEC according to claim 2, further comprising a microphone input line within the housing whereby said microphone input line may receive live, real time analog audio signals.

6. A portable CODEC according to claim 2, further comprising an input line within the housing whereby an analog audio signal may be received from an audio playback device.

7. A portable CODEC according to claim 2, further comprising a voltage level adjuster in the housing whereby the voltage level of an input audio signal on said at least one input line can be adjusted.

8. A portable CODEC according to claim 2 further comprising an analog mixer within the housing, said analog mixer receiving, amplifying and mixing at least two input audio signals to produce said audio input signal to said encoder.

9. A portable CODEC according to claim 2, further comprising a least one audio level display indicator within the housing and indicating when a voltage level of said single input signal exceeds a threshold level.

10. A protable CODEC according to claim 8, 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 amplifier, and

an input mixer mixing amplified audio signals output by said level controllers to produce said audio input signal.

11. A portable CODEC according to claim 8, 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 displays connected to said normal and overload signal detectors, respectively, said normal display when said audio input signal is at said normal threshold, said overload display lighting when said single combined audio input signal is at said overload threshold.

12. A portable CODEC according to claim 2 wherein said encoder encodes said digital input signal based on parameters stored in memory that produce encoded digital signals having a bandwidth range of approximately 20 Hz to 5,500 Hz.

13. A portable CODEC according to claim 2 wherein said encoder encodes said digital input signal based on parameters stored in memory that produce encoded digital signals having a bandwidth range of approximately 300 Hz to 3,000 Hz.

14. A portable CODEC according to claim 2 wherein said encoder encodes said 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.

15. A portable CODEC according to claim 2 further comprising:

an error protection processor adding error protection date to said 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 at said output signal.

16. A portable CODEC according to claim 15 wherein said predefined error protection format is a Reed-Solomon error protection format, said error protection processor providing both burst and random error protection.

17. A portable CODEC according to claim 2 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 an incoming encoded digital signal.

18. A portable CODEC according claim 17 wherein said incoming encoded analog signal contains error protection data, said CODEC further comprising:

an error protection 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.

19. A portable CODEC according to claim 18 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.

20. A portable CODEC according to claim 19 wherein a code of said Reed-Solomon encoder includes code blocks containing approximately 178-bit data words and 8-bit parity words.

21. A portable CODEC according to claim 17 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.

22. A portable CODEC according to claim 21 wherein said processor is selectable by a user between multiple modes of operation, said 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 lossy compression and said lossy decompression routines in stored memory.

23. A portable CODEC according to claims 21 further comprising a clock generator for providing synchronized clock signals to said encoder and decoder.

24. A portable CODEC according to claim 21 wherein said decoder comprises:

memory storing an ISO/MPEG decompression routine; and

a digital signal 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.

25. A portable CODEC according to claim 24 wherein said decoder further comprises:

a D/A converter converting a digital output of said digital signal processor to said analog output signal.

26. A portable CODEC according to claim 25 wherein said decoder further comprises a D/A clock generation unit generating synchronous timing signals for said D/A converter and digital signal processor.

27. A portable CODEC according to claim 2 further comprising:

a headphone amplifier outputting said analog output signal to a headphone output line; and

a volume control controlling the volume of said analog output signal at said headphone output line.

28. A portable CODEC according to claim 27 wherein said headphone amplifier further comprises:

record and local monitor level controls receiving and adjusting levels of said audio input signal and of said analog output signal from said decoder; 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.

29. A portable CODEC according to claim 27 further comprising an analog mixer in the housing providing a mixed audio signal from multiple analog audio sources and wherein said headphone amplifier further comprises:

a record mix controller operative by the user, receiving said mixed audio signal from said analog mixer, said mix controller controlling a level of said audio input signal; and

a record output amplifier controlled by said record mix controller outputting said audio input signal at a desired level to a record output.

30. A portable CODEC according to claim 2, wherein said processor comprises:

a keypad interface adapted to communicate with a keypad and display respectively; and

a microprocessor communicating with the user through the keypad interface.

31. A portable CODEC according to claim 2, further comprising:

a keypad entering input commands to said processor; and

a display displaying responses to said input commands and displaying alert messages.

32. A portable CODEC according to claim 31, further comprising:

a programmable interval timer circuit interfacing said processor with said keypad and display.

33. A portable CODEC according to claim 32, further comprising:

a universal asynchronous receiver/transmitter providing a synchronous input/output data to said processor from an external computer through a remote control port and a serial port in said receiver/transmitter.

34. A portable CODEC according to claim 2, wherein said encoder comprises:

an A/D converter converting said audio input signal to a digital pulse code modulated signal at said 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.

35. A portable CODEC according to claim 34, 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.