Hi Julian, What you say below matches my understanding, and, I believe, what I've said throughout this discussion. Though, I haven't seen RMS used in a DR equation. None of the reference material I have, for audio, signal processing, and engineering in general use RMS for DR...but that doesn't mean some vendor can't make their own equation ;-)
Regards, Austin > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]On Behalf Of Julian > Vrieslander > Sent: Tuesday, June 11, 2002 3:44 PM > To: [EMAIL PROTECTED] > Subject: [filmscanners] Re: Density vs Dynamic range > > > On 6/11/02 2:15 PM, "Austin Franklin" <[EMAIL PROTECTED]> wrote: > > >> In engineering terms you are confusing dynamic range with > signal-to-noise > >> ratio. > > > > Absolutely not the case. Being that I've also designed a LOT of audio > > equipment, I know the difference. They are SIMILAR, but not the same, > > except at one point, when the SNR is at it's highest, it is the same as > > dynamic range. > > For audio and video circuits, SNR usually assumes a standard (or claimed) > reference level, which might be well below the maximum possible signal > level. Say you have a an amplifier stage with a noise level of > 0.0001 volt > RMS. The SNR, relative to a 1 volt RMS reference, is 2 * 10 * > log10(1/0.0001) = 80 dB. The factor of 2 enters, because AC circuit specs > are defined in terms of power levels, and power is proportional to the > voltage squared. > > But that particular circuit might not clip or reach unacceptable > distortion > levels until the signal is increased in amplitude by a factor of 10. The > difference between noise and the maximum possible undistorted > output is 2 * > 10 * log10(10/0.0001) = 100 dB. This is sometimes quoted as the "dynamic > range," and it is consistent with the usage that we have been > discussing in > the scanner context. The difference between the SNR number and > the dynamic > range number is sometimes called the headroom (20 dB in our example). For > an audio component, the headroom spec usually indicates the ability of the > product to cope with signals that exceed the standard or typical levels. > > > SNR also is an RMS based measurements, and RMS doesn't apply > > to dynamic range. > > Why not? I've seen quite a few designers and vendors use the > above-described convention for specifying dynamic range. Consumer HiFi > manufacturers have used other schemes, measuring the limits of their > products to handle impulses or "instantaneous" signals. But usually these > schemes are designed to generate more impressive numbers for > advertisementss. > > This is getting pretty far afield from scanners. > > -- > Julian Vrieslander <[EMAIL PROTECTED]> ---------------------------------------------------------------------------------------- Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body