"These go to eleven."

[ChrisJam]

Hi,

I'd like to know why so many receiver manufacturers mark their volume scales in negative numbers. For example, my Yammy a/v receiver goes from its lowest volume of -99 dB to its max of 0 dB. I have a mini stereo system in my office, and its scale is -76 dB to 0 dB. I saw some amps and receivers in a shop a couple months ago that went from -50 to 50 dB (I forget the brand).

Why have the scale--all or part of it--in negative numbers? So many receivers use the negative numbers that I suspect there must be a logical reason. Do you know what it is?

Thanks,
Chris

 

[MDS]

You are already on the right track because you described the range as a scale. There is no difference between one scale of -99 to 0 vs another from 0 - 100 -> they each have 100 discrete steps between minimum and maximum. The scale with negative numbers is a 'relative' volume display whereas the scale with all positive numbers is an 'absolute' volume display.

The relative scale is more useful for audio because once you calibrate the system to a known output level at a given volume number on the display you can tell at a glance the current output level.

The convention is to calibrate your receiver so that a volume number of 0 is the 'reference level'. Dolby Reference Level is the level to which most recievers are calibrated and that level is 105 dB SPL for the peaks.

So...if you calibrate so that 0 on the volume display yields an output level of 105 dB, when the volume display reads -10 dB you can see at a glance that the peak level is now 95 dB or 10 dB below reference. You can of course calibrate a receiver that uses absolute volume display to reference level too; it is just not as convenient.

As an example, the higher numbered Onkyo receivers let you choose to see either absolute or relative volume display and the manual tells you that 0 on the relative scale is the same as 82 on the absolute scale. If you were to use the absolute scale and use 82 as the reference level, then 72 is 10 dB below reference. That is not as easy as just looking at the display and seeing '-10 dB' directly as you would if you were using the relative display.

 

[ChrisJam]

Thanks

MDS, thanks for a great reply. I get it now!

Chris

 

[bongobob]

I was under the impression that Dolby reference level was 85dB. Am I missing something here?

 

[MichaelJHuman]

Db is a relative (logarithmic) scale not an absolute value (Unless some specific reference such as SPL measured in Db is implied.)

They can set an arbitrary max output level as 0Db and then succesively lower volumes are negative Db.

 

[MDS]

I was under the impression that Dolby reference level was 85dB. Am I missing something here?

If you were calibrating for Dolby Reference Level using a calibration disc like AVIA, you would adjust the channel trims until the SPL meter reads 85 dB but that is because the level of the test tone is -20 dB (which means 20 dB below 'full scale digital'; ie 0 dB). 85+20 = 105. When the musical signal peaks (0 dB), the output level is 105 dB.

If you use DVE or the receiver's test tones, you would calibrate so that the meter reads 75 dB because those tones are at -30 dB.

 

[bongobob]

Any idea why it's done this way instead of having the test tones at true reference level? - B

 

[nibhaz]

Any idea why it's done this way instead of having the test tones at true reference level? - B

105dB of pink noise isn't a real enjoyable experience

 

[MDS]

digital audio level vs reference level

Explaining digital audio levels vs reference level requires a bit of background but here goes...

- 'Reference Level' refers to a specific output SPL; ie the level of the sound reaching your ears. Dolby has defined that to be 105 dB peaks and most people calibrate to the Dolby standards.

- A sequence of bits on a disc have no output SPL until they are turned into an analog signal and amplified (nor do magnetic particles on a tape, the grooves in a record, etc). So it is not possible to record a sound and say 'the level of this sound will be N dB on playback'. However, if you've ever recorded anything you are probably aware that you can set the recording level; ie how 'hot' the signal is recorded. A hotter recording will be louder than a lower level recording when played back at the same volume setting.

Digital Audio Levels

- Digital audio is a sequence of numbers that represent the amplitude of an analog signal at points in time. A CD for example is 16 bit PCM and the analog signal was sampled at 44.1 kHz - meaning that there are 44,100 16 bit numbers for every second of the audio.

- The range of the numbers is determined by the bit depth (16 for PCM on a CD). For CD, they range from -32768 to + 32,767. Those are the maximum negative and maximum positive values for a 16 bit sample. Any sample with the maximum value is 0 dB. 0 dB is the highest level for digital audio - unlike 0 dB SPL which would be the lowest level. (silence).

- After sampling an analog waveform to obtain a stream of bits, the average (RMS) level of that signal depends on how hot it was recorded. If the record level was very high, the average level will be very high. You can think of it as 'potential energy' - just as a tightly wound spring has more potential energy than a loosely wound spring. The average level is some number below 0 dB and because 0 is the highest possible level, the average level is a negative number as in -X dB.

-Modern CDs are VERY hot and typically have average levels around -10 dB. CDs from the '80s typically have average levels around -18 dB. Play the new CD at the same volume setting as the old CD and it will be MUCH louder.

So to relate back to test tone levels: the various calibration discs have the test tone recorded at different levels. AVIA uses -20 dB (which is what Dolby recommends) and that is hotter than the -30 dB that DVE and receiver test tones use. Regardless of the level of the test tone, the output SPL you hear will depend on how much the signal was amplified, how sensitive your speakers are, room acoustics, etc but again playing a tone that is recorded at -20 dB will be louder than playing a tone recorded at -30 dB at the same volume setting on the receiver.

Here is the key point that seems to be missed a lot:
If you use a -30 dB test tone to calibrate the receiver and you adjust until the SPL meter reads 75 dB you will have 75 dB SPL at your ears when the music/movie you are playing has an average level of -30 dB. When that signal hits a peak (the digital value is maximum as explained above) you will have 105 dB SPL.

Now after calibration play a very hot music CD whose average level is already much higher than the level of the tone you used to calibrate the receiver. If that level is -10 dB as are newer CDs, you now have 95 dB SPL average and 125 dB peaks because the average level of that signal was 20 dB hotter to begin with.

 

[rmongiovi]

Any idea why they record hotter these days? Wouldn't that decrease the available dynamic range? (Not to mention, of course, pissing off us old farts with the older CDs who have to move faster than we're used to to turn the volume down....)

 

[MDS]

Any idea why they record hotter these days? Wouldn't that decrease the available dynamic range?

Yes it does. The 'crest factor' is the difference between the average level and the peak level and if you play a new CD and view peak level meters you will see that most new CDs have a crest factor of at most 10 dB.

It's pathetic. Google 'cd loudness wars' for more information.

 

[ChrisJam]

Variables...MDS?

Let me ask some follow-up questions.

1.
Let's assume an amp or receiver of a certain power rating. (I know these rating can vary, based on how they're measured, but that's another issue.) To pick a round figure, let's say an amp delivers 100 w/channel. At its maximum output, it's likely that it'll deliver 105 dB, maximum, if I understand you right, MDS, and assuming the manufacturer goes for the Dolby reference level. But wouldn't speaker sensitivity come into play? Let's say I use this 100 w/ch amp and I drive 8-ohm speakers with a sensitivity of 85 dB/w/m. Then I hook up more sensitive 8-ohm speakers of, let's say, 95 dB/w/m. Given the same maximum power output from the amp/receiver, wouldn't the more sensitive speakers play louder? Assuming the amp/receiver could produce 105 dB with the less sensitive speakers, would it produce over 105 dB with speakers of more sensitivity?


2.
So far I've only owned a/v receivers, no separates. My present receiver is a 100 w/ch 5.1 Yammy. Let's assume its top end--that is, its 0 dB setting--is designed to put out 105 dB. If I try receivers of increasing power--a 150 w/ch receiver (again assuming a true rating) or even a super-powerful amp rated far above 200 w/ch--won't the potential for the maximum sound level rise, too? Could one of these power amps go far above 105 dB?

I do know that having more power means an amp/receiver can coast, whereas a lesser-powered amp/receiver would strain. But what happens to the top end with a powerful amp/receiver?

Thanks,
Chris

 

[MDS]

Such complicated questions! Once again you are right on track with your thinking and hopefully I can fill in the blanks to make it clear. I'm quoting various parts of the question just to keep the context straight.

The first thing to understand is that a receiver/amp is not designed or spec'ed to produce any particular output level. The output SPL you can achieve in your room depends on a lot of factors to which you have alluded: room size and acoustics, power available, speaker sensitivity, distance from the speakers to the listening position, etc.

The power in watts an amp/receiver is spec'ed to deliver depends on the load (speaker impedance) and the majority are specified into an 8 Ohm load because the majority of speakers are 8 Ohm.

Let's assume an amp or receiver of a certain power rating. (I know these rating can vary, based on how they're measured, but that's another issue.) To pick a round figure, let's say an amp delivers 100 w/channel. At its maximum output, it's likely that it'll deliver 105 dB, maximum, if I understand you right, MDS, and assuming the manufacturer goes for the Dolby reference level.

The manufacturer doesn't design the receiver to reach any specific output SPL. The receiver is designed to deliver a given amount of power in watts into a specifed load. Whether or not that 100 wpc receiver can reach Dolby Reference Level depends on all those factors like room size and speaker sensitivity. A 100 wpc receiver in an auditorium won't be able to get anywhere near 105 dB but in an averge size room in a home it may be able to output even more than 105 dB.

But wouldn't speaker sensitivity come into play? Let's say I use this 100 w/ch amp and I drive 8-ohm speakers with a sensitivity of 85 dB/w/m. Then I hook up more sensitive 8-ohm speakers of, let's say, 95 dB/w/m. Given the same maximum power output from the amp/receiver, wouldn't the more sensitive speakers play louder? Assuming the amp/receiver could produce 105 dB with the less sensitive speakers, would it produce over 105 dB with speakers of more sensitivity?

Yes. More sensitive speakers require less power to reach the same output SPL. Doubling the power gives you a +3 dB increase in SPL. Therefore, if you can reach 105 dB SPL using 100 wpc with 90 dB sensitive speakers, you could achieve the same level with 93 dB sensitive speakers using only 50 wpc.

So far I've only owned a/v receivers, no separates. My present receiver is a 100 w/ch 5.1 Yammy. Let's assume its top end--that is, its 0 dB setting--is designed to put out 105 dB. If I try receivers of increasing power--a 150 w/ch receiver (again assuming a true rating) or even a super-powerful amp rated far above 200 w/ch--won't the potential for the maximum sound level rise, too? Could one of these power amps go far above 105 dB?

The 0 dB volume setting is NOT the maximum on most receivers. If the scale is -80 dB to +20 dB, then 0 dB is somewhere around 80% of maximum. That means the receiver will be using roughly 80% of its available rail voltage [I'll save that explanation for later if you are interested]. There is plenty of headroom left between 0 and the maximum but of course as you get closer to the maximum distortion and noise increase.

Using a more powerful amp would increase the maximum possible sound level but remember - double the power equals a 3 dB increase (10*Log(100/50)= 3.01 dB). That is noticeable but not exactly a huge difference.

 

[ChrisJam]

Such complicated questions! [snip]

And such a great answers. I've been thinking about them, and will probably have some follow-ups. But my time today is limited, so I might not get back to the thread until Monday.

Thanks again,
Chris

 

[WorldLeader]

More in response to the thread title, my Logitech z5500 "control station" (pre-amp) will do it's normal volume from 0% to 100% but if you keep turning the knob it will boost from 1 to 10... then 11. I always think it is funny. Of course, you can't listen to music that loud but you can do it when there isn't an active signal.

 

[ChrisJam]

More in response to the thread title, my Logitech z5500 "control station" (pre-amp) will do it's normal volume from 0% to 100% but if you keep turning the knob it will boost from 1 to 10... then 11. I always think it is funny.

I agree. Someone on the design team had a good sense of humor.

Chris

 

[ChrisJam]

Hi, MDS,

The first thing to understand is that a receiver/amp is not designed or spec'ed to produce any particular output level. The output SPL you can achieve in your room depends on a lot of factors to which you have alluded: room size and acoustics, power available, speaker sensitivity, distance from the speakers to the listening position, etc.

OK, I understand. Given the variables, an amp company can only design maximum power into its products, not SPL in the end-user's environment.

Yes. More sensitive speakers require less power to reach the same output SPL. Doubling the power gives you a +3 dB increase in SPL. Therefore, if you can reach 105 dB SPL using 100 wpc with 90 dB sensitive speakers, you could achieve the same level with 93 dB sensitive speakers using only 50 wpc.

Good, that makes sense.

The 0 dB volume setting is NOT the maximum on most receivers. If the scale is -80 dB to +20 dB, then 0 dB is somewhere around 80% of maximum. That means the receiver will be using roughly 80% of its available rail voltage [I'll save that explanation for later if you are interested]. There is plenty of headroom left between 0 and the maximum but of course as you get closer to the maximum distortion and noise increase.

Sure, I understand that any scale would work, as you said in your first reply. I chose -99 dB to 0 dB here because that's what my receiver has and it's what I referred to when I started the thread.

Using a more powerful amp would increase the maximum possible sound level but remember - double the power equals a 3 dB increase (10*Log(100/50)= 3.01 dB). That is noticeable but not exactly a huge difference.

I understand this, I think, and I realize that the dB scale is logarithmic. Let me test myself, and see if I really understand.

Let's assume an amp of 100 watts per channel, designed and measured accurately. It drives an 8-ohm speaker of average sensitivity--let's say 87 dB/w/m. When the amp sends one watt of power to the speaker, the speaker will produce an SPL of 87 dB when measured 1 meter from the speaker's front. (I've learned that there's a little bit of resistance in the system from the wire going from the amp to the speaker, but if the wire is of sufficient thickness, let's assume that this resistance is too small to affect this discussion.)

I learned recently that sound drops off 6 dB with every doubling of distance. (Though I don't understand why sound doesn't follow the inverse-square law.) So if my listening position is 4 meters from the speaker, I've lost 12 dB of sound: 87 - 6 (at 2 meters) = 81 dB, and 81 - 6 (at 4 meters) = 75 dB.

At this point the amp is still sending 1 watt of power. So to get back to 87 dB, I need the amp to add enough power to increase the SPL by 12 dB. It would work like this

1 w = 75 dB/4 m
2 w = 78 db/4 m
4 w = 81 db/4 m
8 w = 84 dB/4 m
16 w = 87 dB/4 m

Or thinking of it another way, for every 10 dB increase in SPL, I need an order of magnitude in power increase from the amp, assuming the same conditions:

1 w = 75 dB
10 w = 85 dB
100 w = 95 dB

On top of that, I can use the amp's volume scale to tell me approximately what percentage of the amp's power I'm using, depending where I am on the scale. Do I have all this right?

Chris

P.S. OK, feel free to hit me with your available rail voltage now.

 

[MDS]

Yep, you understand perfectly.

The simple calculations though leave out the fact that music often has huge transients - like the sudden crash of a cymbal. Transients can require an order of magnitude more power to reproduce perfectly and is why you often want an amp with more power than the simple distance/sensitivity calculations would indicate.

 

[MDS]

rail voltage

I mentioned the rail voltage as an aside because it relates to the misconception that 0 dB on the volume display automatically means some specific output sound pressure level. [I think we've cleared that up in this thread].

The confusion arises, I believe, because many manuals will say something like 'When the test tones are played, the receiver automatically adjusts the volume level to 0 dB'. Now given that 0 dB is the point chosen for the 'reference level', one may conclude erroneously that the test tones are played at 75 dB (the test tones are at -30 dB and 75+30 = 105 dB = ref level).

The amp is designed with a maximum rail voltage - say 40 volts. It can only swing between -40 and +40 volts. The volume control is actually an attenuator - at any point below maximum it is turning down the voltage. As far as I know, the gain applied to the signal is always the same and that is why you can 'clip' an amp if the input signal is too high. If the input signal multiplied by the gain exceeds 40 volts, it gets clipped to 40 volts because that is all the amp can do. Power (watts) is related to voltage so varying the voltage changes the power output.

Now the volume scale is just a range from min to max as we have already established. 0 dB on that scale is somewhere near the max but still quite a bit below it. So what the manual really means when it says that the 'volume is automatically increased to 0 dB' is that the power is at the point between min and max represented by 0 on the display; ie if 0 is roughly 80% of the range, then the power is roughly 80% of max.

 

[ChrisJam]

Combining quotes from two posts

The simple calculations though leave out the fact that music often has huge transients - like the sudden crash of a cymbal. Transients can require an order of magnitude more power to reproduce perfectly and is why you often want an amp with more power than the simple distance/sensitivity calculations would indicate.

and

If the input signal multiplied by the gain exceeds 40 volts, it gets clipped to 40 volts because that is all the amp can do. Power (watts) is related to voltage so varying the voltage changes the power output.

Yes, I left that out of my last post, even though I've read about it. Let's say I have my amp running at 90% of its peak power, and a burst of loud sound would require 20% more power. This is one time when clipping would occur, right? Therefore, I shouldn't run my amp past 80% of its max, and maybe a little less to be safe. And this gets back to earlier posts in this thread about how hot CDs are recorded.

I said in another thread that 2-3 years from now, if we have a house with a larger listening or HT room--right now our 14' x 18' living room serves as as music listening room, HT room, and living room--I'd get better speakers and I'd want a more powerful amp or a/v receiver. We don't need more rooms than we have now, but we'd like larger rooms. A stronger amp would give me the ability to listen to louder volumes without clipping and it'd fill a larger space without straining.

There are times now when I want high SPLs: One is when I'm in the adjacent kitchen cooking or cleaning, and want to hear music. Two is when I'm on my own and want to sit in the living room and have music blasting at me (my gf doesn't like loud music, so I only do this on my own). And three is when we watch DVDs (my gf doesn't mind loud SPL peaks when we watch a DVD). I love having a 5.1 set-up, even if it's just a so-so one by the standards of most of the audiophiles on this forum (but it's far better than a HT-in-box one).

I have a funny story about our 5.1 set-up. We only had a 2.0 set-up (Yammy HRT-5280 a/v receiver and Eosone bookshelves, which are offshoots of Polk & Genesis designed to be sold at a big-box store in the mid-to-late 1990s) until August 2006. I asked my gf for a subwoofer for my birthday. OK, that arrived and I set it up. Nice! Then I found this site and others. I soon found I had to have surrounds and a center channel. We're starting some house remodeling, so we have budget limits this year. I found small, but decent, used surrounds, and I got a new solid center (I did enough research to find one--Polk--that would pretty much match my mains for timbre). The next time another couple who are especially good friends of ours came over for dinner and movie, they brought a movie they picked especially to show off our new 5.1 HT system. They chose the new "King Kong." The first time one of the surrounds kicked in with a blast of sound, the wife in this couple jumped in her chair. She literally jumped, not expecting to hear part of a movie soundtrack coming from beside or behind her at a house.

So that's how new I am to all of this. Before the middle of August I knew nothing of speaker sensitivity or amp wattage (and how it can be misleading) or SPLs. But once I get into something, I'm not satisfied knowing just the basics--how to connect or operate something, for example. I want to know some of the theory, and I want to know enough to teach it to someone else. I appreciate your time in this thread, MDS. I've learned a lot.

Chris