Frequency compander for a telephone line

A frequency compander for improving the frequency response of an audio transmission channel comprising:

• an anti-aliasing filter having an input for receiving an audio signal;
• an analog to digital converter in communication with said anti-aliasing filter to digitize said audio signal;
• a digital signal processor in communication with said analog to digital converter, said digital signal processor executing a computer program which includes steps to compress the frequency spectrum of said audio signal;
• a digital to analog converter for outputting compressed audio from said digital signal processor.

A method for compressing audio information including the steps of:

• (a) inputting an audio signal;
• (b) digitizing said audio signal;
• (c) compressing the frequency spectrum from the digitized audio signal of step (b) into compressed data;
• (d) converting said compressed data to an analog form;
• (e) repeating steps (b)-(d) on a periodic basis.

A method for expanding the frequency spectrum of a compressed audio signal including the steps of:

• (a) inputting a compressed audio signal;
• (b) digitizing said compressed audio signal;
• (c) expanding the frequency spectrum from the digitized compressed audio signal of step (b) into program audio data;
• (d) converting said program audio data to an analog form;
• (e) repeating steps (b)-(d) on a periodic basis.

A method for transmitting audio information between a first point and a second point over a public network connection such that the transmitted audio will be received with a spectral content greater than the frequency response of the public network connection, including the steps of:

• (a) connecting a first frequency compander to a public network at the first point;
• (b) connecting a second frequency compander to said public network at the second point;
• (c) making a connection between said first frequency compander and said second frequency compander on said public network;
• (d) providing an audio program to said first frequency compander for compressed transmission on said public network;
• (e) compressing said audio program in said first frequency compander into a compressed audio program;
• (f) transmitting said compressed audio program on said public network;
• (g) receiving said compressed audio program at said second frequency compander;
• (h) expanding said compressed audio program in said second frequency compander into a restored audio program;
• (i) outputting said restored audio program from said second frequency compander.

A method for selecting a decoding scheme in a frequency compander including the steps of:

• (a) connecting a frequency compander to a telephone line at a first location;
• (b) connecting a remote broadcast device to a telephone line at a second location;
• (c) establishing a connection between said remote broadcast device and said frequency compander over the telephone network;
• (d) transmitting a test tone of a predetermined frequency from said remote broadcast device to said frequency compander;
• (e) determining the frequency of the tone received at said frequency compander;
• and
• (f) selecting a mode of operation based on the frequency determined in step
• (e) from the group consisting of:
• (f)(i) frequency extender mode;
• (f)(ii) frequency companding with shifting mode;
• (f)(iii) frequency companding without shifting mode.

A precision frequency extender for extending the lower frequency range by shifting the frequency of an audio program comprising:

• an A/D converter for digitizing incoming audio;
• a digital signal processor, said digital signal processor receiving digitized audio from said A/D converter;
• a D/A converter in communication with said digital signal processor for outputting frequency shifted audio,
• wherein said digital signal processor performs a series of programming steps to shift the frequency spectrum of said incoming audio according to a trigonometric transformation to create said frequency shifted audio and outputs said frequency shifted audio via said D/A converter.