This is the mail archive of the
cygwin-talk
mailing list for the cygwin project.
RE: SNR calculations (was Re: setup.exe missing from FTP site)
On Sat, 26 May 2007, Dave Korn wrote:
> On 26 May 2007 22:47, Brian Dessent wrote:
>
> > Linda Walsh wrote:
> >
> >>> I prefer to express that as an SNR of -18dB :-)
> >> ---
> >> Could you please show your work!
> >>
> >> I arrived at -9dB. Work:
> >> For each doubling/halving of power one adjusts by ~(+/-)3dB.
> >> (note: "3" is approximation of 10*log(2) or,
> >> to 7 decimal places, 3.010900)
> >> so 1 unit / 2 units of signal would be -3dB,
> >> 1 unit / 4 units: -6dB,
> >> 1 unit / 8 units: -9dB
> >>
> >> From my limited understanding, -18dB would be a reduction of 6
> >> factors of 2, or a 1:64 signal/noise ratio.
> >
> > Typically you use dB to compare the amount of power in a signal relative
> > to a fixed reference; in the case of electronics a common reference is
> > 1mV, or 0 dBmV. Since power in a signal is proportional to V^2, when you
> > compute dBmV from a voltage level it's 20*log(v) due to the power of 2.
> >
> > But when you just want to use dB to represent a unitless ratio, then I
> > agree with you it's simply 10*log(ratio).
> >
> > Brian
>
>
> For purposes of humour, the larger magnitude number is always better.
> Hence I counted 6dB per doubling. The fact that it was technically
> correct is a mere beneficent side-effect!
Also, you must've anticipated this discussion, which surely lowered the
SNR to -18db or less... :-)
Igor
--
http://cs.nyu.edu/~pechtcha/
|\ _,,,---,,_ pechtcha@cs.nyu.edu | igor@watson.ibm.com
ZZZzz /,`.-'`' -. ;-;;,_ Igor Peshansky, Ph.D. (name changed!)
|,4- ) )-,_. ,\ ( `'-' old name: Igor Pechtchanski
'---''(_/--' `-'\_) fL a.k.a JaguaR-R-R-r-r-r-.-.-. Meow!
Freedom is just another word for "nothing left to lose"... -- Janis Joplin