Coming from a Pioneer CD without stopping to think about the dB scale, my initial impression was the the output of the empeg was not as high. i.e. On the old CD 20/40 was really as loud as you want to go while sitting in the car. Where as with the empeg I felt the same level is reached at around -10dB.

I had to then dredge up my lanquishing physics to try and understand what I was looking at. Basically all the voltage change is at the top end.
P = 20 log(V / Vmax), where Vmax is 4V.

So at -6dB the empeg is only at half of its maximum output voltage!

But what does this mean in terms of perceived volume, if I go from -6dB to 0dB, is it twice as loud?

My limited understanding of the decibel scale is that it's logarithmic, and that an increase in 10 means is an increase of 100% in perceived volume. So 70 dB is twice as "loud" as 60 dB. So going from -6 attenuation to 0 would be... uh... less than twice as loud... I think :)

...an increase in 10 means is an increase of 100% in perceived volume.

Take this for what it's worth... based only on what I have been told, with no schooling or scientific evidence to support it, I have heard that a 3 decibel increase results in a doubling of perceived volume. This is the rule of thumb that the SPL lunatics are using, with the the corolarry that doubling the output power of your amps will give you a three decibel gain. This I have observed for myself.

I am perfectly and humbly willing (and waiting!) to stand corrected here.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"

I thought it all depended on what you were measuring. I think it depends if you're interested in magnitude or power. Power is related to magnitude squared, so that's where the 6 db comes from. 3db is equal to doubling normally, I think. db = 10log10( mag / refMag ). The only problem is, I can never remember when you ought to use 20log10(...).

Anyway, the point is that if we perceive a, b, and c as being "equally spaced" volume levels, then when you measure them, you find that a/b == b/c. This could mean a couple of things, and I don't know which. It could mean that our ear responds logarithmically to volume, or, it could mean that our ear responds roughly linearly, and our brain decides that it would be best to compare ratios.

Sorry this is so vague.

Richard.

It could mean that our ear responds logarithmically to volume, or, it could mean that our ear responds roughly linearly, and our brain decides that it would be best to compare ratios.

I think our ear responds logarithmically, so using the dB scale on the empeg actually corresponds to quite a nice linear scale in terms of loudness.

(or I could be full of it...)

I do know that a 3dB increase doubles the power output, or equivalently multiplies the RMS level by 1.4142. But frankly I don't think that a 3dB difference sounds twice as loud...

Michael Grant
12GB Green
080000266

I don't think that a 3dB difference sounds twice as loud...

You are right, of course. The SPL lunatics don't listen to their stereos at all. The only thing they care about is how far up the decibel scale they can go. I was confusing perceived volume with decibels -- three decibel increase = double the power, not double the volume.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"

I think our ear responds logarithmically, so using the dB scale on the empeg actually corresponds to quite a nice linear scale in terms of loudness.

May be our ears do, but our often brains decide differently . . .
Some high-end audio stuff adjust the sensitivity of volume adjustments to how loud the set is playing such that the smallest increments that you can make to the volume, sound equally spaced.

The smallest steps with which you can adjust the gain of a Mark Levinson 380S pre-amp, for example, is 0.1 dB but only between 38.8 and 92.0 dB on the display. Below 38.3 the steps increase, with the largest being a full 6dB (from 7.0 to 1.0)

This works very nice (at least up to 65 dB; anything above that I have never tried) and I'd wish empeg would build something like this into the player.


Henno
mk2 6 nr 6

PS: the steps are:
0.0 1.0 7.0 10.5 13.0 15.0 16.5 17.8 19.0 20.0
20.9 21.7 22.5 23.2 23.8 24.4 25.0 25.5 26.0 26.5
26.9 27.4 27.7 28.1 28.5 28.8 29.2 29.5 29.8 30.1
30.4 30.7 31.0 31.3 31.5 31.8 32.0 32.2 32.5 32.7
32.9 33.1 33.3 33.5 33.8 34.0
from here 0.2 dB until 38.8; 0.1 increments between 38.8 and 92.0 dB

Some high-end audio stuff adjust the sensitivity of volume adjustments to how loud the set is playing such that the smallest increments that you can make to the volume, sound equally spaced.

Thats impressive, I'd be interested to play with that. Someone has obviously done some research (or maths).

Thats impressive.
Yep; works beautifuly

I'd be interested to play with that.
Put it on the wish list!
Also, it should be much easier to implement on a computer based system as the empeg, than having to rig-up resistor banks in analog kit.
I just hope that Hugo/Mike have a look at the table that I included, and play with it. If they do, I'm convinced we'll see something like it in a future release.

Henno
mk2 6 nr 6

This would be more John's kind of thing. You might like to email that table to him (john@empeg.com) and see what he thinks.

Rob

You might like to email that table to him (john@empeg.com) and see what he thinks.

I'll do that (tomorrow).
Good night

Henno
mk2 6 nr 6

The scale used for perceived audio loudness is the dB(A) scale.

One of the few remaining Mk1 owners... #00015

The scale used for perceived audio loudness is the dB(A) scale.

Would you elaborate, please. I have the feeling that there is another one of your superb essays lurking here...

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"

There are a couple of great articles at How Stuff Works on the subject of dB.

They are: What is a decibel, and what is the loudest sound I can listen to before it hurts my ears? and Decibels.

The second article explains when to use 10log and 20log...

-Trevor

-----
Mk 2, Green 12GB 080000349

So somebody explain to me why the empeg volume is negative and goes up to 0?

Calvin

Simple. I think of it this way.

Because you're playing digital music, logically there is a maximum and minimum sample (32767 and -32768). If a sound goes through those it's absolutely 100% loud - you can't get any louder. This remains true all the way up to the DAC. When you turn the volume all the way up, this peak is the loudest sound you want to hear.

It therefore makes sense to call that loudest sound '0dB' - i.e. the point at which the signal has not been touched at all (theoretically). Everything below that is [u]quieter[/u] - so we number down from there, going into negative decibels. Likewise, overdriving that signal (i.e. using positive dB) implies that that peak has been amplified too far and has gone past the maximum range the DAC can convert.

This is the other reason why you adjust your amps so 0dB is the loudest you ever want. That way, that loudest sound is still clear and has no distortion (at least from amplification before the DAC stage). You get much less distortion from scaling the signal down than you get from smashing the peaks past that point of no return. (You do get some, since the signal always has 65536 levels of quantisation and dividing down may mean that two levels get converted into one. For instance, with volume half way, 16382 and 16383 will both get smashed to 8191. But the noise introduced is at -96dB, as I understand it, so you're very unlikely to hear it.)

Make sense?

Save the whales. Feed the hungry. Free the mallocs.

The volume control attenuates the signal. A non attenuated output is therefore 0dB and it goes down from there.

Most consumer stereos display a positive scale, with 0 being silent. If this scale is shown in dB (which it often is) those figures are generally meaningless and have been chosen simply to look nice.

We considered this approach but decided that the more meaningful negative scale was appropriate for the product.

Rob