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Level meter for digitally-encoded audio

  • US 5,751,819 A
  • Filed: 07/24/1995
  • Issued: 05/12/1998
  • Est. Priority Date: 07/24/1995
  • Status: Expired due to Term
First Claim
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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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