Does a spec like this make sense?
 
Noise level, dB (A): -114.9
Dynamic range, dB (A): 112.5
 
I'm having trouble imagining how a device's noise floor can be measured beyond the device's dynamic range.
 
Maybe I'm missing something?
 
Thanks.

you aren't necessarily missing anything... a lot of folks, manufacturers included, have made a real mess of specifications!

Noise level - that's meaningless without a specified bandwidth, although at least they told you they were using a filter (A-weighting). We also do not know how the device under test is configured, but that's a separate gripe<G>!
 
Dynamic Range - again, there isn't enough information here - dynamic range with respect to what?
 
So let's guess that their noise floor number is just that - wide band noise passed through an A-weighting filter. And we'll also guess that the dynamic range is with respect to the noise floor - which is not entirely valid, but it's all we got. So that means that that the device distorts 112.5 dB above the noise floor, which would be a pretty bad specification if it were qualified. But we don't know if they are talking about dBu or dBV or dBFS or dBwtf<G>!
 
There are so many characteristics, and I think you need to know them all in order to understand what they are trying to tell (sell) you...
 
You need to know if measurements are made in the analog or digital domain.
You need to know the nominal operating level - 0VU = +4 dBu for example.
You need to know the maximum operating level, and exactly how it was determined.
You need to know what the noise floor sounds like - is it equal energy across some specified bandpass?
 
Then you need to define S/N or dynamic range...
 
S/N ratio is usually the difference between the nominal operating level and the noise floor at a specified frequency or frequencies. Sometimes it is taken as the difference between a single tone at nominal operating level and the total noise across the band pass.
 
Dynamic range is the actual usable range, and it extends from some maximum operating level (3% THD used to be the magic number, but it is difficult to reach that anymore, so usually the designer will simply measure the THD when the signal swings from rail to rail) to somewhere at, or maybe even below the noise floor, because it turns out we can hear stuff even if it is in the soup.
 
All of this gets even muddier when working within the digital domain, where the maximum level is 0 dBFS because, well, because you can't exceed "all ones". The problem is that too many chip and device designers just assume that if they have x bits they have 2^x bits of dynamic range... and that is not always true.
 
It gets even uglier, since dB is, by definition, an RMS measurement, and digital measurements are, again by definition, peak measurements. So there is some additional math required to make sense of that...

There is are excellent application notes on specifications at the Rane and Audio Precision web sites, among others. I'd suggest a little time with your favorite browser to help clear this up.
 
I spent the entire evening fighting with my computer, so if this is all a bit fuzzy let me know and I'll try to clear it up.

wst3 digital measurements are, again by definition, peak measurements.

I wouldn't say that this is true, strictly speaking.
 
But I think the underlying point is that one must be careful to compare apples to apples when trying to compare specifications.

if you are measuring the instantaneous value, e.g. the value if a single sample, then it is a peak measurement, even if it is not the peak value... which I know sounds ridiculous, but it is what we have to work with<G>. It is, of course, possible to make RMS or even average measurements, over time, but so few people seem patient enough to wait<G>!!

Depends on how they calculate it, I guess.  I think the criteria for measuring noise floor is different than dynamic range.
 
These are also A weighted measurements, which are more perceptual than strict noise levels.   

wst3
if you are measuring the instantaneous value, e.g. the value if a single sample, then it is a peak measurement, even if it is not the peak value

 
You can't have a "peak" unless you are comparing it to something. And if you want to compare it to itself, then it's also the minimum - and the average. 
 
And measuring the difference between samples is not a peak measurement unless you deliberately choose samples to result in a peak. I think the confusion is that digital measurements are very often taken this way whereas this is not the case in analog.
 
And of course in the real world, the "instantaneous" sample value we are considering will often be the result of doing calculations using a number of values measured over time at a lower bit depth and a higher sample rate. But that isn't particularly important, as the result still can be regarded as an instantaneous measurement (even if it wasn't measured that way).
 
 
 
The point is to understand exactly what a specification refers to. 

Sorry for the slow response; I had a long shift on a location shoot.
 
In the example I posted in the O.P. the results are presumably describing an ADC/DAC using a test system where the DAC's output is looped back to the input of the corresponding ADA. The test signal is sent out and returned immediately through a patch cord.
 
The loop includes the analog output and input stage, but presumably the measurements are being made in the digital domain, and I assume involve comparing the original digital data that is fed to the DAC to the resulting digital data that is collected after the return through the ADC.
 
Thanks for entertaining the question and offering insights. I hope the info I just posted may lead to further explanations.
 
best regards,
mike 
 
 

mike_mccue
 
Does a spec like this make sense?
 
Noise level, dB (A): -114.9
Dynamic range, dB (A): 112.5
 
I'm having trouble imagining how a device's noise floor can be measured beyond the device's dynamic range.
 
Maybe I'm missing something?
 
Thanks.
 
 
The loop includes the analog output and input stage, but presumably the measurements are being made in the digital domain, and I assume involve comparing the original digital data that is fed to the DAC to the resulting digital data that is collected after the return through the ADC.

Without knowing exactly what or how they're measuring it's hard to know, but assuming they are using RMS measurements and measuring the noise with no signal present relative to 0 dBFS and using a sine wave to test the DR, the maximum digital sine wave equals -3 dBFS RMS, which would put the DR at a 3dB disadvantage, no?

I had thought about that as a possibility. I guess I've been imagining dynamic range in a digital domain as being an absolute limit and so imagined that a noise floor would be lower than 0dBFS by a fraction of the possible range between *digital silence* and full splat.
 
For example; If a CD player has a theoretical or potential range of 98dB I'd expect to find that the noise floor of the appliance was something like 80dB below full output. That's just a *from the hip* expectation but it leaves me wondering how a spec such as I listed in the OP can seem descriptive of what a user will experience.

mike_mccue
I had thought about that as a possibility. I guess I've been imagining dynamic range in a digital domain as being an absolute limit and so imagined that a noise floor would be lower than 0dBFS by a fraction of the possible range between *digital silence* and full splat.
 
For example; If a CD player has a theoretical or potential range of 98dB I'd expect to find that the noise floor of the appliance was something like 80dB below full output. That's just a *from the hip* expectation but it leaves me wondering how a spec such as I listed in the OP can seem descriptive of what a user will experience.

Not sure how you're getting 80dB there.
 
Assuming no dither, noise shaping or weighting and ignoring any analog noise in the converter, the average quantization error should be within ~3dB of the LSB.
 
If you are taking a weighted measurement, the result will be lower as a portion of the noise will be attenuated by the weighting filter. And if you add noise shaping, the noise shaping will move most of the noise where the weighting filter will attenuate it.