Frequency Compression for Speech Intelligibility
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Solution Overview
Problem
Conventional wireless communications systems suffer from bandwidth limitations that result in the loss of high-frequency information related to consonants, leading to reduced intelligibility of speech signals, especially in noisy environments like cars, where noise masks broadband consonant sounds.
Innovation Solution
A two-stage frequency compression method that moves higher frequency information associated with consonants into a reserved portion of the communication system's passband, preserving consonant information without altering the pitch or tonal qualities of the speech signal, allowing for improved intelligibility even without re-expansion at the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the passband is limited to 300-3400 Hz to meet bandwidth constraints, then bandwidth capacity is preserved, but high-frequency consonant information is lost reducing speech intelligibility
Solution Approach 1:
The patent applies frequency compression to map high-frequency consonant information (above 3400 Hz) into the available passband (300-3400 Hz) by compressing the frequency spectrum. This dimensional transformation allows preservation of consonant information that would otherwise be lost due to bandwidth limitations, thereby improving speech intelligibility without requiring additional bandwidth capacity.
2Object-affected harmful factors
If noise removal or filtering within the passband is applied, then noise reduction is achieved, but intelligibility cannot be improved when noise energy exceeds consonant energies
Solution Approach 1:
The patent applies frequency compression as a preliminary action before noise occurs or as a preventive measure. By compressing the frequency spectrum to preserve high-frequency consonant information in the available passband, the system proactively ensures that consonant information is retained even in noisy environments, rather than attempting to remove noise after it has masked the consonants.
3Loss of information
If linear compression of the entire spectrum is applied to preserve high-frequency content, then high-frequency information is retained, but pitch and tonal qualities are significantly altered
Solution Approach 1:
The patent applies local quality by selectively compressing only the high-frequency portion of the spectrum (above 3400 Hz) while leaving the low-frequency portion (300-3400 Hz) uncompressed. This localized approach preserves pitch and tonal qualities determined by low-frequency vowel formants, while simultaneously preserving high-frequency consonant information through compression of the upper frequency range.
Data Source
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AI summary
A system and method are provided for improving the quality and intelligibility of speech signals. The system and method apply frequency compression to the higher frequency components of speech signals while leaving lower frequency components substantially unchanged. This preserves higher frequency information related to consonants which is typically lost to filtering and bandpass constraints. This information is preserved without significantly altering the fundamental pitch of the speech signal so that when the speech signal is reproduced its overall tone qualities are preserved. The system and method further apply frequency expansion to speech signals. Like the compression, only the upper frequencies of a received speech signal are expanded. When the frequency expansion is applied to a speech signal that has been compressed according to the invention, the speech signal is substantially returned to its pre-compressed state. However, frequency compression according to the invention provides improved intelligibility even when the speech signal is not subsequently re-expanded. Likewise, speech signals may be expanded even though the original signal was not compressed, without significant degradation of the speech signal quality. Thus, a transmitter may include the system for applying high frequency compression without regard to whether a receiver will be capable of re-expanding the signal. Likewise, a receiver may expand a received speech signal without regard to whether the signal was previously compressed.