Would someone please explain how 'gain' functions?

I would appreciate it if someone would explain how gain functions in audio equipment?
I have a 'gain' setting in my phono preamp.  A Gain value (along with loading) is recommended by a cartridge manufacture (MC) for proper function and playback.  So what exactly is 'it' in the electrical world?  What am I changing when I select a particular 'gain'.

When I play my records some are louder on the same volume setting then others.  I find this to be the case on many MFSL and other high quality 180 gram / 200 gram half speed master recordings vs the old school original stamped LP's.

Then there is the difference between loudness of my CD player vs my turntable.  The CD player being much louder than any vinyl playing at the same volume setting.  When I create a CD on my computer with online purchased songs some are very loud and some sound just normal to me at the same fixed volume setting.  I notice the same phenomenon with my Ipod.  Some songs are normal at a volume setting then some songs sound louder.   

I'm not trying to 'fix' anything, just looking for a understandable explanation of the term 'Gain' and how it works.   
Thanks in advance!
As far as gain in reference to phono cartridges, a low output MC will require more gain from the phono amplifier so that when the signal reaches the line stage you don't have to turn up the line stage volume control an excessive amount.  In that instance, selecting a higher gain at the phono amp reduces the resistance to the signal and hence a music signal of higher level going to the line stage or preamp.

In your case, based on what you said about the loudness of CD versus phono playback, you should select a higher gain setting on your phono stage to help equalize the overall volume level of both sources.  You may also benefit sound quality-wise as less resistance is less deleterious to the signal.

Hope this helps.
Gain is a voltage multiplier from input to output.

-6 dB gain = output half of input

0 dB gain = No change.

6 dB gain = output twice input.
Gain is expressed in voltage decibels (dB) which directly translate to SPL dB. So if you used a sound level meter, say to calibrate your home theater, you are using the same units. A change in 6 dB in the audible range requires the voltage to swing by 2.

Technically, electrical dB are calculated from Volts this way :

20 x log ( Vout / Vin )

So for instance, if your Vout is 2x Vin :

20 x log ( 2 / 1) = 6 dB
When you listen to CD’s or streaming audio the gear’s voltages are in the range of 1 volt.

The reason this becomes important for playing back vinyl is phono cartridges generate signals in the range of millivolts (0.001 volt), and MC and MM have very different output levels. Both still much lower than a CD player.

So, as a result, you need extra gain for phono cartridges (in addition to other things) to be compatible with the rest of the audio chain and you need to be able to adjust based on the exact cartridge.

There’s more to all of this, but hopefully this helps.


Gain is the ratio of the output voltage of a component to its input voltage. In the case of a preamp or a line stage or other component having a volume control it is usually defined based on the volume control being set to its maximum position. It can be defined either as a numerical ratio (e.g., 100 times), or in db (db = 20 x logarithm(Vout/Vin); 100x = 40 db).

Usually a CD player or DAC or other digitally-based source component will provide higher output voltages than most phono stage/cartridge combinations, and so the resulting volumes will be different unless the line stage provides independently adjustable level settings for each input.

A factor that can dramatically affect perceived loudness is the dynamic range of the recording, and consequently how much dynamic compression it has been subjected to when it was engineered. Our hearing mechanisms tend to sense volume based on the average level of what is heard, rather than on brief dynamic peaks in volume or on passages that are significantly lower in volume than the average. So if everything else is equal (including the volume control setting) if a recording that has been compressed to a narrow dynamic range (i.e., so that a relatively small difference in volume occurs between the loudest notes and the softest notes) it will tend to sound louder than if the same music has been engineered with minimal or no dynamic compression.

Also, of course, recordings can differ somewhat in the overall volume levels they have been mastered at, even if the music and the amount of dynamic compression are similar.

Regarding phono stage gain, depending on the particular phono stage and cartridge, as well as on the gains and sensitivities of the downstream components including the speakers, there will usually be a relatively small range of phono stage gains that will result in an optimal balance of sonics, noise levels, volume control positions, and avoidance of any possibility of overloading either the phono stage or the preamp. Too much gain or too little gain can adversely affect some combination of these factors.

-- Al
If you lose 6 db at the output, say, when switching from XLR to RCA connectors, is it a lot in real world ? Specifically talking about reel to reel decks.
@Inna, you may be aware of the rule of thumb guideline that a 10 db increase in volume corresponds subjectively to "twice as loud," and correspondingly a 10 db decrease corresponds subjectively to "half as loud."

To provide some additional perspective, for a preamp or integrated amp having a rotary volume control whose minimum position is approximately at the 6:30 o’clock position, and whose maximum position is approximately 5:30 o’clock, a 6 db change will probably correspond to around 45 degrees of rotation. Assuming, that is, that the control is not in the lowest 20% or 25% or so of its range, where volume changes usually occur more rapidly as the control is rotated.

-- Al
My cheap phono pre-amp has a gain control and a little light that goes from green to red depending on the signal. I never know whether to set it so the red flickers from time to time or never.
@N80, I would think the manual should and hopefully would answer that.  Or if not, a call or email to the manufacturer would seem to be in order.

-- Al  
Al, thank you. With my current integrated minimum is at about 6 o'clock and max I don't know. Anything beyond 11 o'clock is unbearably loud with much higher distortion level. My normal range is 7 to 10. So I guess I would be fine if I still used the same amp and speakers.
Hi,  this is Quincy again.

Thanks to all who posted their helpful responses.

So, I have a few more general questions.....

1.  Gain is measured in Voltage dB....what is SPL dB?

2.   Equipment has different Gain voltages.  CD player may have 1 volt.
Why doesn't the pre amp 'level out' or balance all of these different            incoming signals?

4.  Dynamic Range and Dynamic Compression of the signal (Assume both analog and digital) have a major effect on perceived sound levels.  I may have been confusing Gain with these two other items?

5.  On a analog record DR and DC would be either larger or smaller (peak to peak) sound waves embedded in the record groove side walls?

6.  How does DR and DC get put into a digital recording which is really just a bunch of ones and zeros?

5.  Sound is air pressure movement.  How does atmospheric pressure, altitude above sea level, and humidity affect Gain in general?
1) Assuming a speaker is not being overdriven to the point where its behavior becomes significantly non-linear (i.e., "thermal compression" becomes significant), voltage db at any point in the electrical signal path and SPL db produced by the speaker at a given distance will be proportional.

See this writeup for a description of the reference level for SPL db.

2) As I mentioned earlier some preamps provide independently adjustable input level controls. Many and probably most do not, presumably because they would add complexity and cost, and perhaps compromise sound quality. And the user can simply adjust the volume control setting when selecting among different source components.

4) Yes to the statement. Perhaps to the question.

5) Yes.

6) Professional computer-based audio editing programs can easily change the ones and zeros to different ones and zeros corresponding to compression parameters specified by the user.

5) The gains provided by the electronics will not be affected, at least to a degree that is audibly significant. Under some circumstances temperature variations could conceivably affect their gains to at least a slight degree, though. I’m not sure how or if acoustic SPLs might be affected.

-- Al
Thanks Al, this helped quite a bit!  
The link was of particular good help as well.