Level meter for digitally-encoded audio
First Claim
1. An audio level meter instrument comprising:
- an input electronic processing circuit, receiving an input digital audio signal in serial format representing data of a stereophonic audio signal sampled at a predetermined sampling rate, constructed and arranged to derive therefrom an L signal representing left channel audio data and an R signal representing right channel audio data;
a sum processing circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an L+R signal representing an instantaneous sum of the R and L signals;
a display signal processor, receiving as input a subject signal, selected from a group including the L signal, the R signal and the L+R signal, constructed and arranged to process the subject signal in a manner to provide a logarithmic average display drive signal and a logarithmic peak display drive signal, having respective predetermined different ballistic properties;
rectifier electronic processing circuitry means, in said display signal processor and receiving the subject signal, constructed and arranged to act thereupon to apply full-wave rectification to audio data of the subject signal and to thus provide as output a rectified signal representing the audio data of the subject signal in rectified form;
a display drive electronic processing circuit, in said display signal processor and receiving as input the rectified signal, constructed and arranged to act thereupon in a manner to provide as output, an average logarithmic ballistically-conditioned display driving signal representing guasi-average amplitude values of the rectified signal and a peak logarithmic ballistically-conditioned display driving signal representing peak amplitude values of the rectified signal, the two display driving signals being applied to said electronic display device in a manner to enable simultaneous display of quasi-average and peak levels in a co-related and distinguishable manner along a common meter scale;
a digital average detecting process circuit, in said display drive electronic processing circuit and receiving as input the detected signal, constructed and arranged to monitor successive average groups of data thereof each average group containing a predetermined number of audio data samples and to provide therefrom a digital average signal representing the average amplitude of audio data samples contained in each average group;
linear-to-logarithmic conversion means, in said display drive electronic processing circuit and receiving as input the average signal, constructed and arranged to convert linear data of the average signal to logarithmic average data;
a digital average ballistics process circuit, in said display drive electronic processing circuit and receiving as input the logarithmic average data, constructed and arranged to impose a predetermined rise and fall times upon said logarithmic average data and to thus provide the logarithmic ballistically-conditioned average signal;
an electronic display device, receiving as input the display drive signals, constructed and arranged to visually display independent average and peak representations of audio data of the subject signal; and
display drive circuit means, in said display drive electronic processing circuit and receiving as input the ballistically-conditioned average signal, constructed and arranged to operate said display device in a manner to provide a visual logarithmic ballistically-conditioned average display of the subject signal.
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Abstract
For professional audio operations such as recording and broadcasting, an LED bar-graph display instrument monitors average and peak loudness levels of stereophonic audio signals that have been encoded in serial digital format such as AES/EBU digital audio format. Internal audio processing circuitry, that can be implemented digitally with a custom chip gate array set, receives as input a serial stream of digital stereo audio data and converts this to ballistically conditioned logarithmic average and peak levels which are simultaneous displayed, generally simulating the ballistics of contemporary standard electronically displayed loudness meters such as the Dorrough analog model. The peak hold can be switched manually or internally between three hold durations: indefinite, 3 seconds or zero. A preferred dual embodiment provides digital implementation driving a pair of LED bar-graph displays side-by-side in vertical or horizontal orientation for stereo applications, and provides selectable display of stereo signals or sum and difference signals. A special peak capture circuit ensures that even very narrow peak levels are indicated at full amplitude despite the controlled ballistic rise rate. Over-range is indicated by a color change of three top display segments.
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Citations
18 Claims
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1. An audio level meter instrument comprising:
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an input electronic processing circuit, receiving an input digital audio signal in serial format representing data of a stereophonic audio signal sampled at a predetermined sampling rate, constructed and arranged to derive therefrom an L signal representing left channel audio data and an R signal representing right channel audio data; a sum processing circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an L+R signal representing an instantaneous sum of the R and L signals; a display signal processor, receiving as input a subject signal, selected from a group including the L signal, the R signal and the L+R signal, constructed and arranged to process the subject signal in a manner to provide a logarithmic average display drive signal and a logarithmic peak display drive signal, having respective predetermined different ballistic properties; rectifier electronic processing circuitry means, in said display signal processor and receiving the subject signal, constructed and arranged to act thereupon to apply full-wave rectification to audio data of the subject signal and to thus provide as output a rectified signal representing the audio data of the subject signal in rectified form; a display drive electronic processing circuit, in said display signal processor and receiving as input the rectified signal, constructed and arranged to act thereupon in a manner to provide as output, an average logarithmic ballistically-conditioned display driving signal representing guasi-average amplitude values of the rectified signal and a peak logarithmic ballistically-conditioned display driving signal representing peak amplitude values of the rectified signal, the two display driving signals being applied to said electronic display device in a manner to enable simultaneous display of quasi-average and peak levels in a co-related and distinguishable manner along a common meter scale; a digital average detecting process circuit, in said display drive electronic processing circuit and receiving as input the detected signal, constructed and arranged to monitor successive average groups of data thereof each average group containing a predetermined number of audio data samples and to provide therefrom a digital average signal representing the average amplitude of audio data samples contained in each average group; linear-to-logarithmic conversion means, in said display drive electronic processing circuit and receiving as input the average signal, constructed and arranged to convert linear data of the average signal to logarithmic average data; a digital average ballistics process circuit, in said display drive electronic processing circuit and receiving as input the logarithmic average data, constructed and arranged to impose a predetermined rise and fall times upon said logarithmic average data and to thus provide the logarithmic ballistically-conditioned average signal; an electronic display device, receiving as input the display drive signals, constructed and arranged to visually display independent average and peak representations of audio data of the subject signal; and display drive circuit means, in said display drive electronic processing circuit and receiving as input the ballistically-conditioned average signal, constructed and arranged to operate said display device in a manner to provide a visual logarithmic ballistically-conditioned average display of the subject signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An audio level meter instrument comprising:
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an input clock/data recovery circuit receiving an input serial digital audio signal and providing as output a clock signal at a predetermined sampling rate, selected from a group including 32 kHz, 44.1 kHz and 48 kHz, and a reconstituted serial audio data signal; a serial-to-parallel converter receiving as input the clock signal and the serial audio data signal and providing as output L and R signals representing the left and right audio signals respectively; a sum processing circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an L+R signal representing an instantaneous sum of the R and L signals; a difference circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an /L-R/ signal representing an instantaneous difference between the L and R signals; a selector switch constructed and arranged to receive as input the L signal, the R signal, the L+R signal and the /L-R/ signals and to provide as output, and thus cause to be displayed, the subject signal as selected by the user from the four input signals; rectifier electronic processing circuitry constructed and arranged to act upon the data of the subject signal in a manner to apply full-wave rectification thereto and to provide a rectified signal representing audio data of the subject signal in rectified form; an average detecting process circuit receiving as input the rectified signal, constructed and arranged to provide an average signal representing a quasi-average amplitude of the rectified signal; an average ballistics process circuit, receiving as input the average signal, constructed and arranged to impose a predetermined rise and fall times upon the average signal and to thus provide a ballistically-conditioned average display drive signal; a peak electronic processing circuit, receiving as input the rectified signal, constructed and arranged to act thereupon in a manner to provide a peak display drive signal representing peak amplitude levels of the rectified signal; a peak ballistics process circuit, receiving as input the peak signal, constructed and arranged to impose a predetermined rise and fall times upon the peak signal and to thus provide a ballistically-conditioned peak display drive signal; an electronic display device, receiving as input the ballistically-conditioned average and peak display drive signals, comprising a one-dimensional array of LED segments constructed and arranged to display average values in bar graph form and to display peak values in dot graph form as independent representations of corresponding audio data of the subject signal; over-range warning detection means constructed and arranged to monitor audio data of the subject signal, to detect therefrom occurrences of predetermined proximity of audio level data to a maximum audio level limit of the digital audio format and to consequently generate an over-range warning signal, said display device, receiving as an input the over-range warning signal, being constructed and arranged to respond thereto by causing a distinctively recognizable color change in three LED segments disposed at a top scale region of said display device.
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15. A dual audio level meter instrument comprising:
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an input clock/data recovery circuit receiving an input serial digital audio signal and providing as output a clock signal at a predetermined sampling rate, selected from a group including 32 kHz, 44.1 kHz and 48 kHz, and a reconstituted serial audio data signal; a serial-to-parallel converter receiving as input the clock signal and the serial audio data signal and providing as output L and R signals representing the left and right audio signals respectively; a sum processing circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an L+R signal representing an instantaneous sum of the R and L signals; a difference processing circuit, receiving as input the L signal and the R signal, constructed and arranged to provide as output an /L-R/ signal representing an instantaneous difference between the L and R signals; selector means constructed and arranged to receive as input the L signal, the R signal, the L+R signal and the /L-R/ signals and to select as output, and thus cause to be displayed, a pair of subject signals as selected by the user from the following two pairs;
(a) the L signal and the R signal and (b) the L+R signal and the \L-R\ signal;rectification process means, receiving as input the pair of subject signals, constructed and arranged to act upon data thereof in a manner to apply full-wave rectification thereto and to thus provide a pair of rectified signals representing audio data of the subject signals in rectified form; an average detection process circuit receiving as input the pair of rectified signals, constructed and arranged to provide a pair of average signals each representing a quasi-average amplitude of the corresponding rectified signal; a peak detection process circuit, receiving as input the pair of rectified signals, constructed and arranged to act thereupon in a manner to provide a corresponding pair of peak signals representing peak amplitude levels of the corresponding rectified signals; linear-to-logarithmic conversion means, receiving as inputs data of the pair of average signals and the pair of peak signals, constructed and arranged to convert input data from linear to logarithmic form and to provide as output a pair of logarithmic average signals and a pair of logarithmic peak signals; an average ballistics process circuit, receiving as input the pair of logarithmic average signals, constructed and arranged to impose a predetermined rise and fall times upon the logarithmic average signals and to thus provide a corresponding pair of ballistically-conditioned logarithmic average display drive signals; a peak ballistics process circuit, receiving as input the pair of logarithmic peak signals, constructed and arranged to impose predetermined rise and fall times upon the logarithmic peak signals and to thus provide a corresponding pair of ballistically-conditioned logarithmic peak display drive signals; a dual electronic display device, receiving as input the pair of ballistically-conditioned logarithmic average signals and the pair of ballistically-conditioned logarithmic peak display drive signals, comprising a dual array of LED segments constructed and arranged to each display average values in bar graph form and to display peak values in dot graph form on each corresponding array as independent representations of corresponding audio data of the respective subject signals; over-range warning detection means constructed and arranged to monitor audio data of each of the subject signals, to detect therefrom occurrences of predetermined proximity of audio level data to a maximum audio level limit and to consequently generate an over-range warning signal, said display device, receiving as an input the over-range warning signal, being constructed and arranged to respond thereto by introducing a visually recognizable color change in three LED segments disposed at a top scale region of the corresponding array of said display device. - View Dependent Claims (16, 17, 18)
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Specification