Wide dynamic range noise masking compandor
阅读：777发布：2022-04-14
专利汇可以提供Wide dynamic range noise masking compandor专利检索，专利查询，专利分析的服务。并且A noise masking compandor for greatly reducing the noise added to a wide dynamic range audio signal in passing through a noisy channel, such as a tape recorder. The audio signal, having a dynamic range of approximately 90 db, is compressed to a dynamic range of approximately 30 db for transmission through the noisy channel then subsequently expanded in a complementary fashion to its original 90 db range to provide a faithful reproduction of the original signal without noticeable noise. Compression and expansion result from high precision rectifiers to minimize distortion, and are further achieved without the need for maintaining precisely constant input and output levels for the noisy channel to avoid frequency response distortion. A high degree of high and low frequency signal preemphasis is provided in the compression and expansion characteristic without creating overload problems for the noisy channel.，下面是Wide dynamic range noise masking compandor专利的具体信息内容。
1. A noise masking compandor for minimizing the effect of noise in a noisy system, said compandor comprising: means for receiving a signal to be applied to said noisy system; means for preemphasizing predetermined portions of the frequency range of said received signal; means for compressing said received signal as preemphasized by amplification of generally all frequencies thereof to a degree inversely representative of a control signal to provide an approximately 1 db change in compressed signal level for each at least 3 db of change in received signal level; means for developing said control signal in response to the output of said compressing means; said control signal causing said compressing means to provide amplification of said received, preemphasized signal which decreases with the output of said compressing means; means for causing the development of said control signal to be responsive more to predetermined portions of the frequency range of the output of said compressing means; means for applying the output of said compressing means to said noisy system and for recovering the output of said compressing means from said noisy system; means for expanding said compressed, recovered signal in response to a further control signal; means for developing said further control signal for said expansion means from said compressed, recovered signal in a manner similar to the development of the first control signal; and means for complementing the preemphasis in the output of said signal expanding means with a frequency response cHaracteristic providing substantial restoration of the frequency components of said received signal.
2. The compandor of claim 1 further including means for limiting the amplitude excursion of signals at the output of said compressing means thereby to prevent excessive signal levels from reaching said noisy system in response to relatively high frequency transients in said received signal.
3. The compandor of claim 1 wherein said preemphasizing and complementing means provide respectively boost and attenuation to both relatively high and relatively low frequency portions of said received signal and the output of said expanding means.
4. The compandor of claim 1 wherein said means for causing said control signal to respond more to predetermined portions of said frequency range decreases the response of said control signal to portions of the frequency range of said received signal to which said noisy system responds relatively less accurately.
5. A signal compression system of the type operative with a compandor for masking noise in a noisy system, said compression system including: means for receiving a signal to be applied to said noisy system; means for dividing said received signal by a control signal; means for developing said control signal to represent and vary with the output of said divider means; and feedback control means for detecting and reducing the DC level at the output of said divider thereby to reduce DC level shifts in response to changes in said control signal.
6. The compression system of claim 5 wherein: said divider means is of the type having an amplifier receiving as input the signal to be divided and providing as output the quotient of said input and said control signal; said amplifier having its output fed back to its input through a multiplier receiving as multiplier and multiplicand inputs said control signal and the output of said amplifier respectively; said means for reducing DC level shifts at the output of said divider in response to changes in said control signal includes a filter providing DC negative feedback between the output and the input of said amplifier.
7. The compression system of claim 6 further including signal storage feedback means for minimizing the DC level at the output of said amplifier to reduce DC level shifts at the output of said divider in response to decreases in said control signal.
8. The signal compression system of claim 5 further including: cascade filter means for attenuating low frequency components in the output signal of said divider means; and means for preemphasizing low frequency components in said received signal to provide, with said attenuating means, net preemphasis of low frequencies and attenuation of DC level shifts from said divider.
9. An expansion system of the type operative with a compandor for masking noise in a noisy system, said expansion system comprising: means for recovering a signal from said noisy system in a compressed form; means for expanding said recovered signal in response to a control signal; means for developing said control signal in response to said recovered compressed signal to provide expansion of said recovered, compressed signal complementary to the compression thereof; said developing means being operative to augment the expansion of said expanding means in response to high volume components at predetermined frequencies in said recovered, compressed signal thereby to augment crescendo effects in the expansion of said recovered, compressed signal.
10. In a noise masking compandor of the type having signal compression and signal expansion systems for respectively applying a compressed signal to and recovering a compressed signal from a noisy channel, means for developing a control signal for said expansion and compression systems including: means responsive to said compressed signal for providing precise peak rectification thereof; Means for filtering the rectified signal to provide said control signal; the filtered rectified signal having fast attack and slow decay characteristics; means for causing the fast attack characteristic to be operative in response to increases in said compressed signal in excess of predetermined percentages of the filtered, rectified signal; and means for providing in said fast attack characteristic reduced rectification switching delay and relatively fast response time with respect to the rates of variation of said received signal.
11. The system of claim 10 further including means for amplitude limiting of said compressed signal above a predetermined signal amplitude thereby to prevent overloading of said noisy channel before said control signal is effective to produce a signal amplitude reduction through said signal compression system.
12. The system of claim 10 wherein said compandor includes: a plurality of signal channels with respective signal compression and signal expansion systems; each of said respective signal compression means being operative in response to the same control signal; each of said respective signal expansion means being operative in response to the same control signal; and means for combining the compressed signals applied to and for combining the compressed signals recovered from each of said signal channels to produce respective single compressed signals for developing said control signals for compression and expansion.
13. The system of claim 12 wherein said compressed signals combining means includes a summing network.
14. The system of claim 12 wherein said compressed signals combining means includes means for selecting as each of said single compressed signals the highest of the compressed signals applied to and the highest of the compressed signals recovered from each of said signal channels.
15. The system of claim 10 further including means for limiting the amplitude range of said control signal to signal levels between predetermined upper and lower signal level limits thereby to produce compansion over a substantially limited range of signal levels.
16. The compansion system of claim 10, further including one or more compression system means for causing said control signal to be developed over a limited range of signal levels which provides for significant improvement in signal to noise ratio and for pleasant sound reproduction of said compressed signal without signal expansion.
17. In a noise masking compandor of the type having signal compression and signal expansion systems for respectively applying a compressed signal to and recovering a compressed signal from a noisy channel, means for developing a control signal for said expansion and compression system including: an operational amplifier receiving said compressed signal; means for providing buffer amplification; first means for providing rectification connected between the output of said operational amplifier and said buffer amplifying means; second means for providing rectification connected between the input and output of said operational amplifier with the connection between said first and second rectifying means being between terminals thereof which are of opposite characteristics; signal storage means connected between the input of said buffer amplifying means and the input of said operational amplifier; said signal storing means having a slow decay characteristic; negative signal feedback means connected between the output of said buffer amplifying means and the input of said operational amplifier; means for receiving the output of said buffer amplifying means and providing parallel low-pass filtering thereof and attenuation to a predetermined percentage; second buffer amplifying means responsive to said low-pass filtered signal for providing as an output thereof said control signal; difference amplifying means for amplifying the difference between said signAl attenuated to a predetermined percentage and the output of said second buffer amplifying means; and means for rectifying the output of said difference amplifying means and for conducting the output of said difference amplifying means to the input of said second buffer amplifying means whenever said signal attenuated to a predetermined percentage exceeds the output of said second buffer amplifying means.
18. The system of claim 17 further including feedback means from said buffer amplifying means to said low-pass filtering means for causing a more rapid response by said low-pass filtering means.
19. In a noise masking compandor of the type having signal compression and signal expansion systems for respectively applying a compressed signal to and recovering a compressed signal from a noisy channel having emphasis of predetermined frequencies, means for developing a control signal for said expansion and compression system including: signal equalizing means responsive to said compressed signal for providing relative signal enhancement at frequencies in which said noisy channel has emphasis and providing relative signal attenuation to frequencies at which said noisy channel has relatively inaccurate signal response characteristics; and means for fast attack, slow decay peak rectification of said equalized signal to provide said control signal.
20. The system of claim 19 adapted for audio frequency range compression and expansion and wherein said signal equalizing means includes means for providing its relative signal enhancement at generally high frequency and generally low frequency portions of the audio frequency range and to provide its relative signal attenuation at generally higher frequencies and generally lower frequencies respectively as compared to said frequencies of signal enhancement.
21. The system of claim 19 further including: means for providing signal preemphasis in advance of the application of said compressed signal to said noisy channel; means for providing signal deemphasis complementary to said signal preemphasis after signal expansion; the frequencies of signal preemphasis and deemphasis being at least partially coextensive with the frequencies of relative signal enhancement of said equalizing means.
22. A noise masking signal compression system for minimizing the effect of noise in a noisy channel having prescribed preemphasis, said system comprising: means for receiving a signal to be transmitted by said noisy channel; means for preemphasizing predetermined frequencies of said received signal; means for amplifying the preemphasized signal to provide an amplified output in response to a control signal; said amplifying means including a feedback path having a multiplier responsive to both the amplified output and said control signal; means for attenuating low frequency portions of the variably amplified signal to provide in combination with said preemphasizing means, net low frequency emphasis; means for amplitude limiting the variably amplified signal to prevent overloading of said noisy channel; means for applying the attenuated, limited signal to said noisy channel; means for emphasizing said applied signal at frequencies at least partly corresponding to frequencies preemphasized by said noisy channel; means for providing precision, full wave, peak rectification of said emphasized signal with fast attack and slow decay characteristics; said fast attack characteristic having a response with reduced rectification switching delay and having a response time as fast as all but the fastest varying portions of said received signal; means for nonlinearly filtering said peak rectified signal to provide low-pass filtering thereof in response to variations in said peak rectified signal which do not exceed said low-pass filtered signal by a predetermined percentage and to provide fast attack response to variations in said peak rectified signal which do exceed said Low-pass filtered signal by said predetermined percentage; and means for squaring said nonlinearly filtered signal to produce said control signal.
23. The noise masking signal compression system of claim 22 wherein said control signal is limited in amplitude range to cause compression of a fractional portion of the amplitude range of said received signal.
24. The noise masking signal compression system of claim 22 including: means for recovering said applied signal from said noisy channel; and means for expanding an equalizing said recovered signal with a characteristic complementary to the compression, low frequency attenuation and pre-emphasis of said received signal; and means for augmenting expansion of said recovered signal to provide augmented crescendo effects.
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