From: ruffrecords@yahoo.com   
      
   Arny Krueger wrote:   
   > "Ian Bell"  wrote in message   
   > news:hnrl37$qq4$1@localhost.localdomain   
   >> Arny Krueger wrote:   
   >>> "Ian Bell"  wrote in message   
   >>> news:hnp8nc$4o3$1@localhost.localdomain   
   >>>> Arny Krueger wrote:   
   >>>>> "Ian Bell"  wrote in message   
   >>>>> news:hnmbmi$p5e$1@localhost.localdomain   
   >>>>>   
   >>>>>> 0dB has no meaning.   
   >>>>> Actually, it does. In the digital domain 0 dB is   
   >>>>> commonly equated with FS.   
   >>>> No, that is 0dBFS.   
   >>> Yes, so your use of the word "no" must be some kind of   
   >>> terrible mistake on your part.   
   >>>   
   >> No, 0dBFS refers to full scale signal in a digital   
   >> system.   
   >   
   > Of  course!   
   >   
   >> It is common, especially in live recording to set   
   >> '0dB' to -15dBFS so as to ensure sufficient headroom. In other words, 0dB   
   >> can be anything you like and therefore   
   >> on  its own without context is meaningless.   
   >   
   > Ian, you seem to be fascinated with telling people that they are wrong, and   
   > then explaining it by reciting either the exact same facts they did, or   
   > paraphrasing them.   
   >   
   >>>>> While the units are arbitrary and may be confusing to   
   >>>>> people who still think 100% analog, it is both   
   >>>>> meaningful and commonly used.   
   >   
   >>>> No it is not.   
   >   
   >>> Assertion without support, which should be immediately   
   >>> dismissed.   
   >   
   >> OK, then we will dismiss your original unsupported   
   >> assertion that 'it is both meaningful and commonly used'.   
   >   
   > Tit for tat?   
   >   
   >>>>>> Input termination in both cases is unspecified.   
   >>>>> If the input is a mic input, then the usual standard of   
   >>>>> 300 ohms applies.   
   >>>> It is a power amp, it does not have a mic input. 300   
   >>>> ohms is NOT the 'usual standard for a mic input'   
   >>> Good modern power amps are common, and do not have that   
   >>> much variation in their noise performance with normal   
   >>> variations in source impedance.   
   >   
   >    
   >   
   >>>>> If the input is a line level input, then the source   
   >>>>> impedance is usually such that system performance is   
   >>>>> not affected that much by probable variations.   
   >>>> You miss the point. How is the input terminated when   
   >>>> noise is measured - obviously it is not left open   
   >>>> circuit is it?   
   >   
   >>> I guess you've never measured the actual noise coming   
   >>> out of a good modern power amp with the normal range of   
   >>> source impedances. They often don't vary all that much.   
   >>> Remember, this is not legacy vacuum tube equipment which   
   >>> was generally far noisier.   
   >   
   >> A 'good modern one' should not vary much. We have no idea   
   >> if the OPs's device falls into this category. However, if   
   >> the noise is being minimised then a point will be reached when the source   
   >> impedance is relevant because if the amp was extremely   
   >> noise free that would be the ONLY source of noise.   
   >   
   > Baseless speculation.   
   >   
   >> OTOH, it will not vary much with source impedance if the   
   >> amp is very noisy to start with, like an old tube amp. SO precisdely   
   >> the coinverse of what you state is in fact true.   
   >   
   > I thank you for substantiating a point I make below.   
   >   
   >>>>>> Output termination is unspecified.   
   >>>>> The noise performance of line level outputs is   
   >>>>> minimally affected by probable  and reasonable   
   >>>>> variations in load impedance.   
   >>>>>> No bandwidth is specified.   
   >>>>> Relevant and already mentioned   
   >>>>>   
   >>>>>> No weighting or not is specified.   
   >>>>> Relevant and already mentioned   
   >>>>>   
   >>>>>> No mention of whether the measurements are rms, peak,   
   >>>>>> quasi-peak   
   >>>>> Both SNR and DR are ratios of two measurements. It is   
   >>>>> most important that both measurements be done under the   
   >>>>> same circumstances.   
   >>>> In fact they generally are not since a signal and noise   
   >>>> have quite different characteristics. The signal will be   
   >>>> measured rms. The noise can be measured in several ways   
   >>>> each giving a different figure.   
   >>> While people could be stupid and compare a noise level   
   >>> measured in peak-to-peak volts to a signal measured in   
   >>> average volts, I know of no actual cases where this   
   >>> happens, except perhaps in your mind, Ian.   
   >   
   >> No, but as I keep saying, manufacturers will show their   
   >> product in the  best light and judicious use of weighting and bandwidths   
   >> will alter the 'measured' value considerably. 'A'   
   >> weighting, which is pretty commonly used by manufacturers will often   
   >> improve and amplifiers   
   >> noise spec. by 10dB.   
   >   
   > Believe it or not, "A" weighting has a reasonble justification. It weights   
   > the noise in accordance with the response of the human ear at the levels   
   > that noise from a reasonably clean piece of equipment is likely to be heard.   
   > It properly focuses on noise at frequencies where the ear is more sensitive,   
   > and tends to give less weight to noise at frequencies where the ear is less   
   > sensitive.   
   >   
   >>> There   
   >>> could be equipment noise that has a high crest factor,   
   >>> but nature does not usually go down that path.   What is   
   >>> then left is a few dB of ambiguity, and most good modern   
   >>> equipment (which is common) is not so noisy that a few   
   >>> dB is a deal breaker in actual use.   
   >   
   >> It is more than 'a few dB'   
   >   
   > Baseless assertion.   
   >   
   >   
   >>>>  >> Variations in the way the above are specified canmake a   
   >>>>>> large difference to the 'measured' value   
   >>>>> Some yes, some no.   
   >>>>>>  and I bet you   
   >>>>>> can guess which set the marketing department will want   
   >>>>>> to choose.   
   >   
   >>>>> One other benefit of the solid state/digital revolution   
   >>>>> is that SNR and DR performance is often so good (> 100   
   >>>>> dB) that most variations in how they are mentioned   
   >>>>> don't matter that much.   
   >   
   >>>> Rubbish.   
   >>> Dismissive, unsupported claim, again itself worthy only   
   >>> of dismissal.   
   >   
   >> As I have said before DR and SNR are not the same and   
   >> they have little relation to the actual level of noise   
   >> heard in the speaker.   
   >   
   > Ian, I've shown many ways that just your say so is not relevant or binding.   
   > Come up with some authority other than yourself, or watch your whole   
   > discussion flush down the toilet.   
   >   
   >> The OP's amp for instance has an   
   >> output power of 800W. Suppose this is into a load of 4   
   >> ohms then this requires over 56V rms output signal. The   
   >> DR is 100dB so the noise at the output is 100dB below 56V   
   >> rms which which works out at  a mere -65dBu.   
   >   
   >   
   > The good news is that nobody in their right minds hooks 800 watt power amps   
   > up to lines where 0 dBu is the reference level. IOW Ian, your example is   
   > irrelevant to good, reasonable practice.   
   >   
   >> The original all tube Leak Point One in 1949 had a   
   >> measured output noise and hum of -80dB below 10W into 15   
   >> ohms which works out at just over 12V rms. So its output   
      
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