Wadia S7i direct to amp

12-04-10: Bombaywalla
wrong! every 6dB (i.e. every 12 steps) is halving of the voltage amplitude. You correctly wrote that the digital amp works in the voltage domain & not the power domain but you did not understand that concept fully.

actually, you are incorrect. the basic decibel measurement is computed as follows:

10*log10(q1/q2)

where q1 and q2 are quantities that are being measured
(ref: http://en.wikipedia.org/wiki/Decibel).
[wikipedia is not a peer-reviewed reference so you always have to view statements there with some degree of caution, so feel free to challenge this statement if you have a better reference - i just don't feel like digging through my own books since the wikipedia equation matches my own knowledge on the subject]

as it turns out, power is proportion to voltage**2. so when the quantities being measured are power levels, and since power is a function of voltage, the equation for power can also be represented as a ratio of voltages:

10*log10((vo**2/r)/(vi**2/r))

[i am assuming equal resistance values for simplicity]

however, because of the way that logarithms work, you can also express this equation:

20*log10(vo/vi)

this is the equation that you presented - i'm just trying to explain to you how the equation was derived. so, a 3dB reduction in voltage corresponds to a 6dB reduction in power.

you will notice that the wadia white paper refers to *volume* output. volume output is a power domain concept. so the wadia white paper on digital volume control indicates that you start to lose significant (i.e. non-interpolation bits) when the digital attenuation causes a 36dB reduction in *volume* output.

i took a look at the wadia manual, and i think that there is an error in the manual. the manual states that there is a 0.5dB change in *volume* for each step in the digital volume control. from my calculations, and the wadia white paper on digital volume control, it appears that there is actually a 1dB change in volume for each step in the digital volume control.

so, a 3dB reduction in voltage corresponds to a 6dB reduction in power.

wrong! a 3dB reduction in POWER corresponds to a 6dB reduction in VOLTAGE.

i took a look at the wadia manual, and i think that there is an error in the manual.

I had a good laugh at this one!!! :-)

it appears that there is actually a 1dB change in volume for each step in the digital volume control.

Oh, is it??
so, now we have 100 steps & 100dB of volume control??
You better call up Wadia & tell them that they actually have 100dB of volume control & not 50dB.....

Paperw8: a 3dB reduction in voltage corresponds to a 6dB reduction in power.

Bombaywalla: wrong! a 3dB reduction in POWER corresponds to a 6dB reduction in VOLTAGE.

I haven't taken the time to read through most of this thread, but I'll just say with respect to the quoted comments that neither is correct.

A 3db reduction in power corresponds to a 3db reduction in voltage, for a given impedance. A 6db reduction in power corresponds to a 6db reduction in voltage, for a given impedance.

To see that, consider that a 3db reduction in voltage corresponds to the voltage being reduced by a factor of 0.707. Since, as I think we all agree, P = Esquared/R, that 3db reduction in voltage results in power being reduced by a factor of 0.707 x 0.707 = 0.5, which is also 3db.

Regards,
-- Al

12-05-10: Bombaywalla
wrong! a 3dB reduction in POWER corresponds to a 6dB reduction in VOLTAGE.

unlike much of the subjective discussion in this forum, this is a factual matter; your *opinion* on the matter is irrelevent to the actual *facts*.

12-05-10: Almarg
I haven't taken the time to read through most of this thread, but I'll just say with respect to the quoted comments that neither is correct.

A 3db reduction in power corresponds to a 3db reduction in voltage, for a given impedance. A 6db reduction in power corresponds to a 6db reduction in voltage, for a given impedance.

the reason why impedance is not considered is because you are generally looking at power at a given point. for example, when you measure output power, you are always measuring power at the output terminals, so there is no difference in impedance. in this case, what we are describing is the effect of the wadia digital volume control on either the voltage output level or on power output level. so if you do a decibel measurement on voltage, the voltage level is halved at each 3dB increment; if you do a decibel measurement on the power level, that too is halved at each 3dB measurement, but if you look at power as a function of voltage and perform the power measurement AS A RATIO OF THE CORRESPONDING VOLTAGE LEVELS, then each halving of voltage level corresponds to a 6dB redunction in power level (you need to pay particular attention to the capitalized section).

at this point i have to say that i think that i have explained this as best i can. so if someone still isn't following this, then i can't help them and they will have to refer to other sources for further discussion.