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#1
Posted to rec.audio.tech,rec.audio.pro,comp.dsp
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dBFS
"Randy Yates" wrote in message
What units would a typical professional digital audio system use to measure RMS values of digital signals? The well known DAW software packages Cool Edit Pro and Adobe Audition both have a measurement tool that produces both peak, average, and RMS values. The measurement interval is the range of the wave that is selected and highlighted on the screen. They provide their measurements in dB FS. Signal values in DAW programs are typically dimensionless because they are dependent on the gain of the ADC that was used to digitize them, perchance they once existed as analog voltages. The gain of ADCs is not standardized and is often not even carefully specified. Pro audio ADCs often have continuously-variable analog or digital attenuators on their inputs. If you stabilize the settings of the input attenuators, then Pro Audio ADCs can be calibrated. I use an analog meter and sine waves for the purpose. The RMS and peak values of a dimensionless quantity are themselves both dimensionless. |
#2
Posted to rec.audio.tech,rec.audio.pro,comp.dsp
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dBFS
some comments: 1) Any meter can be calibrated to read the RMS value of a steady sine wave. i.e. Simpson 260 reads the RMS value of a steady sine wave but is not true RMS responding. 2) True RMS meters will read the RMS value of any (within its limitation) STEADY waveform i.e. a steady square wave or steady triangle wave etc. 3) There is no standardized reading of RMS for a time varying waveform like real audio, as has been mentioned the integration time and weighting needs to be defined and I don't think there is such a standard? 4) dBFS meters on most digital equipment are not RMS or average but are more peak reading, that (try to) capture the peak value of even an individual sample. 5) Most of us given a choice I suspect would choose to a dual meter system, one that shows both the peak so that we can be assured there is no clipping combined with another display that show the LOUDNESS. LOUDNESS is not the same as RMS. There are some standards on metering of loudness of audio. Those are the two reasons we meter audio, to assure the equipment is not overloaded even on peaks and for some gauge of the loudness. Note: As has been discussed in another thread on intersampling peaks, even the definition of peak is ambiguous, the peak SAMPLE value is not always the same as the peak value of the reconstructed waveform. I don't know, but I suspect that most peak meters calibrated in dBFS are reading the peak SAMPLE value and not the true wavefomr peak therfore the true audio peak can be even higher. I don't know if this is what Randy is trying to get at or not. Mark |
#3
Posted to rec.audio.tech,rec.audio.pro,comp.dsp
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dBFS
"Mark" wrote in message
some comments: 1) Any meter can be calibrated to read the RMS value of a steady sine wave. i.e. Simpson 260 reads the RMS value of a steady sine wave but is not true RMS responding. Yes, and most of the meters in use, whether as test equipment or part of a piece of audio gear, is average-responding, calibrated as if it was RMS. IOW as we both knows, its only accurate for sine waves. 2) True RMS meters will read the RMS value of any (within its limitation) STEADY waveform i.e. a steady square wave or steady triangle wave etc. That depends on the TRMS meter. In another post I pointed out that some DAW software metering facilities respond to the portion of the wave that is selected which can range from a whole song to one or just a few samples. 3) There is no standardized reading of RMS for a time varying waveform like real audio, as has been mentioned the integration time and weighting needs to be defined and I don't think there is such a standard? I'm pretty comfortable with the metering in my DAW software because it leaves the integration time up to me and delivers both peak and average readings. 4) dBFS meters on most digital equipment are not RMS or average but are more peak reading, that (try to) capture the peak value of even an individual sample. Yes, or they respond to both peak and average values. 5) Most of us given a choice I suspect would choose to a dual meter system, one that shows both the peak so that we can be assured there is no clipping combined with another display that show the LOUDNESS. LOUDNESS is not the same as RMS. There are some standards on metering of loudness of audio. I have a lot of equipment and software that works this way. Those are the two reasons we meter audio, to assure the equipment is not overloaded even on peaks and for some gauge of the loudness. Agreed. Our ears response is closely approximated by True RMS as calculated over various periods of time. Note: As has been discussed in another thread on intersampling peaks, even the definition of peak is ambiguous, the peak SAMPLE value is not always the same as the peak value of the reconstructed waveform. I've been aware of this issue for years. I take intersample peaks to be freaks of nature that respond well to being ignored. I don't know, but I suspect that most peak meters calibrated in dBFS are reading the peak SAMPLE value and not the true wavefomr peak therfore the true audio peak can be even higher. I don't know if this is what Randy is trying to get at or not. Some software applies a Sinc function to the samples and integrates under it. |
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