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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!
quincy

Showing 1 response by erik_squires

erik_squires
5,268 posts
 
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.


Best,
E

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