My first question has to do with the integrated amplifier I got a couple months ago (it's an older model). Amongst the various switches and what not on it are two knobs that perform what I thought was the same function: One knob is labelled "Volume". The other smaller knob is labelled "Loudness" Does anyone know what the difference is, because I sure as heck don't.

My second question is one I don't know how to word for a search. On a lot of amps and receivers I've seen, the most comfortable volume is around -50dB ~ -30dB (depending on the source). What is the definition of 0dB?

Thanks,

Just a guess here, since I had an amp which also had a "loudness" thingy. On mine it was for adjusting the frequency response in such a way that high and low frequencies are amplified when you turn it up. Does it sound like that?

It could be used to compensate for the lowered sensitivity of our ears for these frequencies at low sound levels. Google Search

1) Loudness button: The loudness setting is dependant on manufacturer decisions: it can amplify the bass or the bass & the treble by a number of dB so it sounds 'better', on some amps works only when the volume is kept down and is dynamically 'reduced' when rising the volume to avoid clipping. (example - Bass: 6dB boost @120Hz Treble:3dB boost@10kHz - for a certain integrated amp when you press the loudness button).

2) How loud is 0dB volume: 0 is maximum - no attenuation. Again, some receivers may use digital attenuation (which would suck in case it has 16bit DA/AD);

Every receiver has a preamp & power amplifier included besides the DSP thingie that lets you select Dolby Prologic or whatever. Anyway, 0 would be max (the full output of the pream is fed into the amp). If the manufacturer took care not to clip the amp at that settings its another question...

The perceived volume depends on lots of factors:
- CD loudness (RMS)
- CD player's output VRMS
- preamp gain/sensitivity
- amplifiers final stage gain (most are near <30dB).

What about when the little meter goes up above 0 db? IIRC my amp continues up to +18 dB. How does this fin in with the theory that 0 dB is full output without attenuation?

The Amplifier in question is a Yamaha A-720 Integrated Stereo Amplifier. I'm inclined to think that the loudness dial (and it IS a dial, not a button) follows ErikS's explanation more than Lucpes, if only because the amp already has a bass & treble dial (which I happily keep at 0 ).

I probably should have kept browsing Yamaha's site before asking that question, since their pre-amp manual basically explains it.

Two more amp related questions.
1. My amp has a button that says "Auto Class A" It doesn't sound any different when it's enabled, but the amp does seem a bit hotter (as is normal for a class A amp). What's the point of this though?

2. As far as I can tell, pre-amps do all the work. What exactly is the point of a seperate normal amplifier?

Again, thanks for all the answers

'Loudness' is supposed to boost bass or bass & treble, boosting more at quiet volumes to compensate a bit for how our ears work, and boosting less as you raise the volume. Usually this is just a button. Some give you a dial so you can adjust the relative amount of boost to tailor it more to your liking. So if you think it is boosting too much, you can turn the boost down a bit, and vice versa.

Sorry for that I just explained what 'traditional' loudness switch does (older gear). Don't know for sure about newer ones but I guess it does the same, but using a potentiometer to achieve variable gains.

+18dB must be there because the preamp is used to further amplify the signal from the inputs.

Separates are used because there is (usually) an improvement from having separate power supplies; there are constraints of (relatively) low power devices like a preamp (line-level signals, <500mW) and (relatively) high power devices (speaker-level, 10s or even 100s of Watts) such as an amplifier.

Just to expand slightly on what has already been stated... yes, the knob on your receiver is a variable version of the more common loudness button. It was a feature for many years on Yamaha receivers and integrated amplifiers of the "Natural Sound" range (and may still be, I haven't looked closely at any Yamaha equipment in some time).

Loudness buttons or controls are meant to compensate for the human ear's variable sensitivity at different frequencies, as plotted by the "Fletcher-Munson curves", a statistical averaging of listening tests compiled some years ago. We tend to be less sensitive to bass and treble at low volumes compared to the midrange. So one way to compensate and make music sound more "natural" at low volumes is to bump up the bass and treble.

Whereas most makers of audio equipment that chose to implement this feature put it in the form of a button (ideally to be pressed only when listening at low volumes), Yamaha built a variable circuit that gradually boosts the required frequencies as you turn the volume down - so the maximum effect is obtained when the knob is turned counter-clockwise.

As I recall from the user manual of a friend's rig many years ago, Yamaha recommends calibrating and using the thing like this: with the main volume knob turned all the way down, crank the smaller loudness knob all the way up. Then turn the volume knob back up until the music is as loud as you're likely to ever want it. And leave it there. From now on, use the smaller loudness knob to adjust your volume instead of the normal volume knob - as you turn your music down to quieter levels, the bass and treble are gradually boosted so you can still hear them properly.

It's a neat trick if you can remember which knob to turn

Of course my memory may have failed me on a detail somewhere; apologies if your amp behaves differently from what I described, but I thought it might be worth passing on.