I'm just making up a number.
 
I'm relating it to times when I have had systems turned up loud enough to actually hear a noise floor... which I guess relates to the entire system and it's sensitivity. 

My (overly simplistic) view:
Any piece with a noise-floor of -115dB is pretty darn quiet.
As a result, I'd expect it to have pretty wide dynamic range.

With analog stuff the dynamic range is defined between some described threshold of noise at the quiet end of the range and some defined threshold of distortion at the loud end of the range.
 
I guess I have assumed that digital stuff has a dynamic range within the confine of its bit depth and I also assumed that the noise floor will be somewhere above the quietest value that the bit depth can theoretically describe.
 
I know I am confusing something... just haven't figured it out yet.

drewfx1You 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. 

Not trying to be difficult, but can you explain that please? As far as I know it is absolutely possible to make peak, average and RMS measurements without comparing it to anything other than the scale (e.g. volts, spl, etc). And if you compare it to itself then what's the point? I'm really missing something in your statment...
 

drewfx1And 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.

 
There are differences in measurement techniques between the analog and digital domains. But I"m not sure what that has to do with measuring the difference between samples, or why that would be considered a peak measurement.
 

drewfx1And 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).

 
So I am definitely missing something here... please elaborate. To me any given sample is an instantaneous value, that is what sampling is all about... measuring the instantaneous value at time "t". Bit depth and sample rate have nothing to do with the level, except that for a given word length there will be a finite number of possible values.
 

drewfx1The point is to understand exactly what a specification refers to.

Well this is certainly true! And probably the biggest stumbling block the audio and MI marketplaces face.

There are so many terms, standards, definitions, etc that I thought I would share my definitions, now that I have a minute...
 
Noise Level: where to start??? Noise level is a wide band measurement, and takes into account all noise energy present under some specified (we hope) conditions. Among other things, the actual band pass being measured, any weighting filters employed, and the condition of the inputs and outputs should be specified.
 
A reasonable specification might read: noise level = -96 dBu from 20 Hz to 20 kHz, C-weighting applied, all inputs terminated with 150 ohms, all outputs driving  passive 1 Mohm loads.
 
Dynamic Range: the ratio, in dB, of the loudest (undistorted, but then of course you should define undistorted) signal to the quietest discernible (and again, we need a way to define this, since we can hear signals in the noise) signal. The fact that we use dB suggest that this is an RMS measurement. The measurement is made by measuring the wideband noise with no signal present, and then measuring the signal at the clip point (however clip point is defined). This approach does not take into account the fact that we can discern signals buried in the noise floor, but we just don't have a reasonable objective method to do so yet.
 
A reasonable specification might read: Dynamic range = 108 dB from 20 Hz to 20 kHz, no weighting filters applied. Maximum level measured 0.1% THD across the same passband. From this we can calculate the noise floor. Alternately, we could specify the noise floor, but we still would not know what was happening when we reached the maximum operating level.
 
Signal to Noise Ratio (SNR or S/N): the ratio, in dB, from some reference level (by consensus the nominal operating level or 0 VU) to the noise level. For a really meaningful measurement it is a good idea to state the gain in addition to reference level, bandwidth, and filters applied.
 
A reasonable S/N ratio might read: S/N ratio = 96 dB from 20 Hz to 20 kHz, A-Weighted. Excitation signal 1 kHz @ +4 dBu, unity gain, input shorted for noise measurement. Again from this we can tell that the noise floor is 96 dB below the nominal operating level, or approximately -92 dBu, across the pass band.
 
Headroom: The difference, in dB, between the nominal operating level and some maximum operating level, usually the clipping point, but once again it is helpful to define the clipping point. Any gain should also be listed.
 
A reasonable headroom specification might read: Headroom = 22 dB from 20 Hz to 20 kHz with respect to +4 dBu, at 1 kHz, clipping = 3% THD from 20 Hz to 20 kHz.
 
There are other related terms, but I didn't have as much time as I thought<G>... questions and comments welcome.

wst3

drewfx1You 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. 

Not trying to be difficult, but can you explain that please? As far as I know it is absolutely possible to make peak, average and RMS measurements without comparing it to anything other than the scale (e.g. volts, spl, etc). And if you compare it to itself then what's the point? I'm really missing something in your statment...

 
Peak implies "highest" or "maximum", no? "Highest" compared to what? Simple as that. 
 

 

drewfx1And 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.

 
There are differences in measurement techniques between the analog and digital domains. But I"m not sure what that has to do with measuring the difference between samples, or why that would be considered a peak measurement.
 

 
I didn't really write what I was getting after very well.
 
In digital, when we are talking about a "peak" we are generally referring to the highest (positive or negative) valued sample compared to all the other samples in the period of interest. Is there any other definition of "peak"?
 

drewfx1And 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).

 
So I am definitely missing something here... please elaborate. To me any given sample is an instantaneous value, that is what sampling is all about... measuring the instantaneous value at time "t". Bit depth and sample rate have nothing to do with the level, except that for a given word length there will be a finite number of possible values.

 
OK, say our ADC is outputting 24 bits at 48kHz. Given that oversampling - often at a higher rate and a lower bit depth - is common, that means our instantaneous sample value output by the ADC at 48kHz at time "t" is a calculated value based on the values of many samples over a period of time - perhaps a thousand samples or more. The point is that the calculation does not involve taking the peak value of all the input samples, so why would we call it a peak measurement?
 
 
It's not a big deal. I just don't understand why you would want to call each sample a peak measurement.

I think I've been comfortable regarding a "discrete" sample as a "peak" measurement because I equate it to a near instantaneous voltage measurement which seems unlike my Volt Ohm Meter which purportedly measures voltage with a true RMS function.
 
As a reminder, a measurement of voltage must be referenced to two points, so of course any measurement of voltage must be referenced to something. We usually call the reference point circuit ground and I suspect that everyone taking part in this discussion knows that this reference may or may not coincide with earth ground.
 
Having said that I don't really know what the time range is for the voltage measurement function of either my demonstrably sluggish Volt Ohm Meter or my seemingly fast acting MOTU 896HD. Drew's point about oversampling offers me some clues about what I haven't previously considered.
 
I guess, for myself, the idea that the final result of a ADC is written to a database as a discrete sample makes it seem like a peak or instantaneous measurement, and this idea will be hard for me to shake but I think I can appreciate what Drew has made a point of stating more specifically.
 
Now, I'm wondering if one should consider the circumstances separately when speaking about the ADC and the DAC. Is there any such thing as oversampling in DAC processes?
 
 
 
You guys do a great job of pushing me forward in understanding stuff.
 
Thanks to all of you for making comments and observations!!!

drewfx1Peak implies "highest" or "maximum", no? "Highest" compared to what? Simple as that.  

I think you are mixing domains a bit here, and that leads to poor use of terms, which can lead to confusion.
 
Peak voltage refers to either the maximum point in a periodic waveform over one cycle, or the maximum voltage of a non-periodic waveform over some defined period of time. These are definitions that are agreed upon by standards bodies, much like the SI measurement system. Sure, there are folks that try to re-use them for other purposes, but that leads to confusion. In both cases there is no reference, the comparison is to all other values during the measurement period.
 
Chief amongst the points of confusion is the fact that when you start making measurements in the digital domain you have so many new possibilities!!! I mean you have the whole dang thing stored for starters!! It's almost enough to make one's head spin.
 
For example, in the analog domain the common ways to measure distortion involve either the use of a really sharp filter to remove the excitation, or a swept filter. Neither of these involves storage because, historically, about the best we could do for analog storage was a long persistence phosphor<G> (and yeah, they were fun to read! Towards the end of the analog era there were instruments that combined really sharp band stop filters with really sharp band pass filters that were adaptive, but mere mortals could not, generally, afford such toys.
 
Once we have digitized the signal it becomes a simple matter of math. You want total harmonic distortion, or would you like to break it down by harmonics? And trust me, the latter is far more informative if you are designing or troubleshooting.

drewfx1In digital, when we are talking about a "peak" we are generally referring to the highest (positive or negative) valued sample compared to all the other samples in the period of interest. Is there any other definition of "peak"?

 
Which is pretty much what I said. There is no reference other than the measurement period.
 

drewfx1OK, say our ADC is outputting 24 bits at 48kHz. Given that oversampling - often at a higher rate and a lower bit depth - is common, that means our instantaneous sample value output by the ADC at 48kHz at time "t" is a calculated value based on the values of many samples over a period of time - perhaps a thousand samples or more. The point is that the calculation does not involve taking the peak value of all the input samples, so why would we call it a peak measurement?

 
We call it a peak measurement because we simply do not care about the calculations. We care about the word as presented to the DAC, or the word generated by the ADC. You are right about over sampling, and single bit converters, but these things do not matter with respect to audio specifications. Audio is analog, and it always will be as along as our ears are analog. (OK, our ears are not analog, but we treat them as such because there is so much we still don't understand about the ear-brain system... but that's drifting way far off track!)
 
We care about a LOT of different things when it comes to audio, I didn't even bring up crest factor, for example, because that tends to cause even more confusion. Crest factor is defined as the peak to average ratio of a periodic waveform, but we use it to describe pink and white noise sources all the time. These are supposed to be random, which kind of kills the whole periodic bit, except that they are not random at all. They can be generated from a semiconductor junction, or even a resistor, but over time we discover that even these are not truly random. Forget about MLS based noise generators, they can't be random... but all of these can be random enough for use as excitation signals for audio tests. And we can, if we are very careful, talk about the crest factor of the noise source. We have to if we want to characterize an audio system.
 
And that's the last piece of the puzzle - are we looking at a component, a circuit, or a system? And are we talking about analog or digital or both?
 

drewfx1It's not a big deal. I just don't understand why you would want to call each sample a peak measurement.

Actually, it is a big deal. There is a remarkable amount of misinformation out there. Some of it is well meaning, some of it is meant to mislead consumers. All of it makes it that much more difficult for the good guys to develop and provide high quality devices and systems.
 
If that makes any sense...

There may be some confusion as to what Dynamic Range means in a slightly different context. When one starts to get interested in Loudness Meters you tend to come across the Dynamic Range Meter measuring process as well. In this context it is not the ratio between 0 dB FS and the noise floor.  It is very much something else.  It is much more about the loudest parts of the music related to the softest parts so this could be the context to which Dynamic Range refers.
 
Check this article here on how the TT Dynamic Range meter works:
 
http://www.dynamicrange.d...suring%20DR%20ENv3.pdf
 
So if the average loudest part of the music reaches say -6 dB  but the softest sections may get down as far as -20 db then the average DR measurement will be 14. Maybe people are confusing this form of dynamic range measurement to the standard max 0 dB FS down to the noise floor measurement which will be very high and easily be able to handle the other more interesting and useful DR measurement. Stop thinking measuring the medium and think measure the music instead. More interesting and way more useful. Especially in a mastering situation where you are trying to make tracks loud by increasing their rms levels but still maintaining a decent DR measurement. There is a sweet spot where both will be satisfied. But over that it starts to get too loud and the DR suffers badly.

Jeff - good point, and in fact the dynamic range of an audio recording, or performance, is a very different thing.
 
But Mike's original question was specifically about a device specification!
 
Specifically, he asked if the following made any sense:
Noise level, dB (A): -114.9
Dynamic range, dB (A): 112.5
 
And in fact it doesn't, this is a silly, and meaningless specification because it does not provide enough information.
 
We can guess all day long, and the most reasonable guess is that the noise floor, across the usable bandwidth of the device, is 114.9 dB below some specific reference level, sadly we do not know what that level is.
Further, we can guess that the clipping point (also not specified) is 112.5 dB above that noise floor, but we don't know whether it was measured at a single frequency or across the entire usable bandwidth.
 
In this case, if the noise level is measured with respect to the nominal operating level then the clipping point falls somewhere below the nominal operating level - that would be pretty bad!
 
If, instead, the specification is using full scale output as the reference then the clipping point occurs approximately 2.4 dB below 0dBFS, which is still bad, but I've certainly run across designs that clip in the analog domain before they clip in the digital domain.
 
And, in fact it really makes no difference whatsoever how narrow or wide the dynamic range of a performance or recording might be if the equipment can not handle it! So I guess I think it is important to measure the medium. I've certainly attended more than enough live performances that far outstrip the capabilities of all but the very best recording chains in terms of dynamic range, so if I were recording such a performance I'd want to know what the medium is really capable of.
 
It really is not sufficient to say that a converter chip has 24 bits of resolution - some of the lowest order bits are going to be in the noise floor, and therefore of no real use to anyone. And, as in the example Mike provided, if the upper most bits cause the analog circuit to clip, well, then they aren't much use either.
 
Poor use of terminology only serves the marketers!
 
OK, rant over, time to go back to yard work...