[Elegiac]

Alright.
If I input 2.1vrms into a device which then applies a gain of 0.96, or a loss of -0.35 db, to the signal, would I then be outputting about 1.8 vrms?
Trying to nut this out, and this is the closest I feel I've come so far. Any advice would be much appreciated.

 

[71 dB]

Alright.
If I input 2.1vrms into a device which then applies a gain of 0.96, or a loss of -0.35 db, to the signal, would I then be outputting about 1.8 vrms?
Trying to nut this out, and this is the closest I feel I've come so far. Any advice would be much appreciated.

Input = 2.1 Vrms
Gain = 0.96
Gain in decibels = 20*log10 (0.96) = -0.35 dB
Output = Input * gain = 2.1 Vrms * 0.96 = 2.016 Vrms

In decibels it would go like this:

Input = 2.1 Vrms = +6.44 dB (V)
Gain = 0.96 = -0.35 dB (V)
Output = 2.1 Vrms * 0.96 = +6.44 dB (V) - 0.35 dB (V) = 6.09 dB (V) => 2.016 Vrms

 

[Elegiac]

Input = 2.1 Vrms
Gain = 0.96
Gain in decibels = 20*log10 (0.96) = -0.35 dB
Output = Input * gain = 2.1 Vrms * 0.96 = 2.016 Vrms

In decibels it would go like this:

Input = 2.1 Vrms = +6.44 dB (V)
Gain = 0.96 = -0.35 dB (V)
Output = 2.1 Vrms * 0.96 = +6.44 dB (V) - 0.35 dB (V) = 6.09 dB (V) => 2.016 Vrms

Thanking you. Just checked and it's actually 2.3 volts input, which is even better.
I think I'm safe. I don't like losing voltage in this case, because I'll be pushing 600 ohms.

I got my answer using my usual flair for math:

 

[71 dB]

Thanking you. Just checked and it's actually 2.3 volts input, which is even better.
I think I'm safe. I don't like losing voltage in this case, because I'll be pushing 600 ohms.

I got my answer using my usual flair for math:

The gain is in decibels here (0.96 dB) which make sense. Be careful about the numbers being on dB-scale or linear scale.

 

[Elegiac]

The gain is in decibels here (0.96 dB) which make sense. Be careful about the numbers being on dB-scale or linear scale.

Intuiting a bit here based on descriptions... but, the 'reference voltage' is according to a 'linear' scale? Whereas your calculations are 'db-scale'?

I'm assuming your working out is more correct than my trawling through calculators and converters til I find something that seems to work.

 

[Elegiac]

No, that's not right. Reference voltage just... doesn't seem to be applicable. Not the value I'm looking for.

 

[71 dB]

Intuiting a bit here based on descriptions... but, the 'reference voltage' is according to a 'linear' scale? Whereas your calculations are 'db-scale'?

I'm assuming your working out is more correct than my trawling through calculators and converters til I find something that seems to work.

Voltages such as 2 V, 1 V or 750 mV are on linear scale, but they can be expressed on logarithmic dB-scale if we have a reference voltage. For example if our reference voltage is 1 V, we get for the mentioned voltages:

2 V => 20*log10 (2 V/1 V) = 6.02 dBV
1 V => 20*log10 (1 V/1 V) = 0 dBV
750 mV => 20*log10 (0.75 V/1 V) = -2.50 dBV

Gain is output volltage / input voltage. The input voltage is the reference voltage. "How many volts do you get out for every volt you put in?" So, if input voltage is 0.76 V and output voltage is 0.32 V, the gain is 0.32 V/0.76 V = 0.42 on linear scale and 20*log10 (0.32 V/0.76 V) = -7.5 dB on logarithmic scale.

 

[Elegiac]

It's beyond me, ahaha. That calculator seems sorta pointless to me now as well. If reference and input are the same, then the distinction between linear and logarithmic must be why the same value can be entered twice. And the reason for all this is beyond me.

I've just been using this: ???*10^(???/20) to work out voltage output for things. The first value being input and the second being gain. Found it somewhere and I copy paste it into the google search bar Doesn't seem to work here though.

 

[71 dB]

It's beyond me, ahaha.

These things tend to be beyond people who don't have proper education.

That calculator seems sorta pointless to me now as well. If reference and input are the same, then the distinction between linear and logarithmic must be why the same value can be entered twice. And the reason for all this is beyond me.

You need to understand what you are calculating.

I've just been using this: ???*10^(???/20) to work out voltage output for things. The first value being input and the second being gain. Found it somewhere and I copy paste it into the google search bar Doesn't seem to work here though.

Your equation is correct, but note that gain has to be given in dBs. The 10^(???/20) hassle is transferring the dBs into linear scale.

So, if your input voltage is 2.0 V and gain is 3.3 dB, you calculate the output voltage: 2.0 V * 10^(3.3/20) = 2.9 V

In the calculator the reference voltage doesn't mean any "input" of any device. It is just reference that the input voltage is compared to: 2.1 V has a 0.96 dB gain compared to 1.88 V.

 

[castleofargh]

@Elegiac
There is no reason to be lost anywhere. Initially your gain didn't specify a unit so @71 dB considered it a simple multiplier of the voltage

2.1 Vrms * 0.96 = 2.016 Vrms

It's that dumb. If you see specs of an amp with a 2X gain, then it can double your input voltage. It's completely straightforward IF the gain value was indeed just a multiplier for the voltage.


But gain can also be expressed in dB and your screenshot clearly shows a gain calculated in dB from the clear "gain (dB)" in the calculator next to the 0.96 line. Which if correct, makes @71 dB's first post incorrect, as he assumed like I did that a gain without unit was a coefficient to directly multiply by the input voltage to know the output.

Personally I would always write a gain as +6dB or 2X. That way there can be no confusion about unit. As he warned, you just have to know which one you're looking at and all is well.

 

[Elegiac]

Oh I see! That makes sense. In regards to the calculator.

And I just realised why I wasn't getting a meaningful result from my usual equation.
I was doing this: 2.1*10^(0.35/20)
When I should have done this: 2.1*10^(-0.35/20)
Which gets me basically what you worked out.

 

[Elegiac]

@Elegiac
There is no reason to be lost anywhere. Initially your gain didn't specify a unit so @71 dB considered it a simple multiplier of the voltage

It's that dumb. If you see specs of an amp with a 2X gain, then it can double your input voltage. It's completely straightforward IF the gain value was indeed just a multiplier for the voltage.


But gain can also be expressed in dB and your screenshot clearly shows a gain calculated in dB from the clear "gain (dB)" in the calculator next to the 0.96 line. Which if correct, makes @71 dB's first post incorrect, as he assumed like I did that a gain without unit was a coefficient to directly multiply by the input voltage to know the output.

Personally I would always write a gain as +6dB or 2X. That way there can be no confusion about unit. As he warned, you just have to know which one you're looking at and all is well.

Well, what I'm working with is this:

This is an excerpt from a long correspondence, in which I had to wade through layers of nonsense, as far as I can tell. But I have the device figured out now.

Just wanted to know how much voltage it was costing me at this point.

 

[WoodyLuvr]

What an awesome thread! Polite. Helpful. Informative. Interesting. Hoping for more like it!

 

[gregorio]

Oh I see! That makes sense.

It’s really easy to get confused with dB and linear scales, even pros occasionally get caught out!

Obviously the dB scale is logarithmic but it also represents a ratio and there are about 50 different dB scales. So with the root-power scales (such as dBV), a linear factor of double = +6dB, while with a power scale, such as dBW (Watts) a linear factor of double = +3dB. Then there’s the issue of ratio to what? With dBFS it’s the ratio to digital full-scale (0dBFS), with say dBSPL it’s a ratio to 20 microPascals (0dBSPL) and so on but it can get confusing quickly because many of the dB scales have some relationship with others, for example: 0dBu is referenced to 0.775v which into 600Ohm results in 1mW and is also the reference for 0dBm but dBm is a power scale and dBu is a root-power scale. Even dBFS can be confusing because there are different specifications for the output voltage of 0dBFS. For example, in some countries the TV specs are -20dBFS = 0dBVU = +4dBu = 1.228v but in others it’s -18dBFS = 1.228v and with music it can be anywhere from -20dBFS = 1.228v to -12dBFS = 1.228v and that’s for pro-audio DACs, consumers ones can be almost anything.

Hope I haven’t confused you more, just trying to illustrate that confusion with dB is easy, even if you know a fair bit about it!

G

 

[Elegiac]

Well, for my purposes, a lot of amps give the gain in just... decibels? High Gain = 16.5db, for example. I don't know which of the 50 that is.