DFT spectrum and coefficient insight

"Jerry Avins" <jya@ieee.org> wrote in message 
news:eb2dnQ1z1ZGRiJvVnZ2dnUVZ_gudnZ2d@rcn.net...
> bulegoge@columbus.rr.com wrote:
>
>
> It's not an explanation of details that's needed, but an understanding of 
> the fundamentals. I'll try to help.
>
> A decibel is a ratio of powers. It is a tenth of a bel; one bel represents 
> a power ratio of ten, the familiar "order of magnitude".
>
> Ten decibels also represents a power ratio 10, so 20 dB is a ratio of 100, 
> and so on. A table of logs will show that a ratio of 4 is about 6 dB. The 
> formula is dB = 10*log10(power ratio).
>
> In linear systems, power at any given node is proportional to the square 
> of voltage, so (power ratio) = (voltage ratio)^2. Observe that if
> 10*log10(power ratio) = 10*log10((voltage ratio)^2), then it also equals 
> 20*log10(voltage ratio).
>
> The various subscripted dB types are named for different references. A 
> power of 1 milliwatt = 0 dBm. On a 600-ohm line, that represents a voltage 
> of .7746; sqrt(.6). .7746 volts on any impedance = 0 dBu. Note that when 
> computing dB from voltage, the multiplier is 20. 0 dBm = 0 dBu in a 
> 600-ohm circuit.
>
> I'd be happy to try to clarify any of that if is wasn't as helpful as I 
> would have liked.
>

Jerry,

Thanks for the thoughtful inputs.

Brent