more headroom with 24 bit

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wes480

wes480

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I am using an Aardvark Q10. It has its own separate mixer software, that has peak monitors and such...and tells you when you are clipping the preamps.

My question is, if I am recording in 16bit vs. 24 bit in Logic...I should be able to record a higher level with 24bit....but, my Aardvark mixer is going to say the same level is clipping...regardless of what I am using in Logic.

There arn't any options that I see on the mixer to tell it if I am using 16bit, or 24 or whatever. I guess those meters on the Aardvark are always going to clip at a certain level...and I will just have more headroom in 24bit that I couldn't even get to with the Aardvark? Bleh...I am confused!! Becuase it is a 24bit capable card.
 
I always figured the headroom thing with 24-bit was not that you could record louder, but that you could record softer and there would still be less quantization noise than if you were at 16.

For example, if you were recording at a certain level in 16-bit so that you didn't end up using the last four bits, well then you'd be at 12......

but if you were to do the same thing in 24 and not use the last 4 bits, then you'd be at 20...

I don't know if I'm making any sense...
:confused:
 
0db is a hard limit when it comes to digital so you don't gain any headroom there. Where you do gain headroom is your noise floor drops down. What this basicly means is that you don't have to ride your gain to -1db you can record at -20. That way you have 20db of headroom before cliping and you don't have any noise to worry about.
 
wes, you might be confusing headroom with dynamic range or maybe i'm wrong.
 
Wes..Use your software mixer the same..regardless of what bitrate your at.
 
then explain this

I too believe that 0dB is 0dB and no bit depth change will let yourecord louder before clipping, but I am struggling to understand something about this:

I just tried my first 24 bit recordings last night with my new Audiophile card and was seemingly able to set signal levels way beyond the previous limits using 16 bit recording with a SB. What gives?

I first used Pro Tools Free @ 24 bits, dithered that down to 16 bits and then did some editing with Cool Edit. It was in Cool Edit that I noticed all the peaks should have been overmodulated, but they weren't. Am I being misled by my VU meters? I then tried 32bit floating point recording with Cool Edit and confirmed that I can't trust my signal level meters any longer. I get no clipping when I go way beyond the 0dB threshold. Can anyone explain this?

thanks
 
ok...well, use the mixer the same...that works.

yes what was said about quan errors and noise floors etc is all true....but, with 24bit...you do have a higher maximum recording level...even though it is referenced at 0db - the actual signal is still louder..

I don't think I am wrong on that...perhaps I am though.
 
Wes, sorry you are wrong. You can record lower not higher. Your loudest sounds will always be 0. But with 16bit if your floor was at -50db it would be around -70db in 24bit (those numbers are just for example).

The 'Headroom' comes in if you want to record at a lower level like the other guys suggested. Based on the noise floor example above you could record at -20db in 24bit and still have the same SNR as 16bit and still have 20db of 'headroom' left over just in case.

I think Mackie confused the whole headroom issue because that was a big part of their sales pitch. In their case they are talking about headroom over 0db but before distortion. That is only possible with analog and not digital. So a Mackie may have an extra 8db of headroom beyond 0 but digital never goes beyond 0.
 
right right right...but you are missing my point.

"digital never goes beyond 0"

thats becuase digital is referenced at 0, to make it easier with changing standards to always know that 0db is your max point...your clipping point.

But, with 16 bits, you get 96db of Dynamic range....at 24bits you get 144db.

In the "real world" (meaning not digital references)...you can never record lower than what we have....we can already record at "nothing"...(to what level we have to get to to hear...or notice...etc...whole different issue..and not my point).

With 24bit recording...I can record up to 144db (referenced at 0db in digital), with 16 bit I can record only to 96db (referenced at 0db in digital) - ...I can get a louder signal with 24bit.

So, back to my question - how does that relate to preamps? I assume each preamp has its own "clipping point" that is separate from whatever the recording medium is capable of.

"You can only record to 0" is not the answer...becuase whatever "0" is is going to depend on what bit depth you are recording at.

Now...I am not trying to sound like I know it all...becuase I have no clue...I'm just really confused. But...24 bit is 144db....which means that in 24bit recording....0db = 144....I am having a hard time making the practical connections with this.

I havn't been able to do 24bit recordings yet....in theory...I would think recording the same signals etc, that in 24bit, I would be recording at like -20db....I'm sure that's not right though.
 
You've reversed the whole db scale for your explanation. 0 is 0. 0 will vary in actual listening db depending on whatever volume the listener sets.

For the sake of argument you cant really get 144db of dynamic range due to the limitations of physics and analog speakers and mics. The extra bits are more for computational value and lower noise floor.

Your argument makes sense in a "pass the bong and think about it really hard" type of way but you are reading too much into it and trying to define 'headroom' which is not really a scientific term anyway. If that helps your understanding of a fairly loose term than more power to ya ;)
 
heh, Ed already went through this (kind of) on the thread titled "Volume".

I guess I am just not going to be able to understand the answer I am after for now...

I understand that the noisefloor gets lower...but, that doesn't mean that 24bit doesn't allow for a louder signal.

I don't know. I'm just going to have to wait until I can play with 24bit recording before I can even hope to understand it.

But, the one fact is that 0db is the maximum signal in digital...whether it is 60db, or 96db, or 140...0 is just a reference to the loudest possible signal - which will vary depending on bit depth.
 
Another way to look at it would be; if you had a converter that reached it's o db maximum record level with, say 1 volt from the mixer at 16 bit mode, and you could switch it to 24 bit mode, it would still reach max 0 db at 1 volt, but the converter noise would be lower.
The 24 bit option alows a bigger voltage difference between 0 db max and the noise. Where we put that voltage range is determined at our analog gain stages.

(I'm not an expert here, just one of the students)
See ya
Wayne
 
alright. well, obviously i am just not getting it. I am gonna forget about this until i start doing some 24bit recordings ;)
 
wes:

just remember 0 db is always 0 db. 16, 20, 24 bit, it is all the same peak level: 0 db. with 24 bit, you have more space between your noise floor (the bottom) and 0 db (the top).
another way to think about it is with the paint program that comes with windows, and adobe photoshop. if you draw a picture in paint, and draw the same picture in photoshop, you will say photoshop has a more detailed picture, even though if you maximize both windows, they are both the size of your screen. the picture is not bigger. it is just more detailed, and therefore better. it has to do with the programming that goes into the program. the same for 16 bit and 24 bit audio. the sound does not get bigger. BUT there is alot more space UNDER the maximum level... therefore "more headroom", and more detailed sound.
 
Does anyone have a sound file of comparisons?

Like the same guitar line, or trumpet or something recorded with a version of 16, 20, and 24 bit to show the difference in sound?
 
Brian, there is no difference in sound. Just a lower noise floor. The main difference will be when you add effects and mix. That is where the extra bits help in the DSP calculations and the lower noise floor helps the total mix.

DVD uses 24bit audio.
 
TexRoadkill said:
Brian, there is no difference in sound. Just a lower noise floor. The main difference will be when you add effects and mix. That is where the extra bits help in the DSP calculations and the lower noise floor helps the total mix.
Click to expand...

Really?? No difference in sound even after putting down several tracks? What about like decays on, say, a sustained piano chord ringing out until the end, when it's really soft? I'm interested in hearing if anyone's done a test comparison between a 24-bit and lesser-bit (software, I guess) session where everything else was equal -- like going thru the same card capable of at least 20-bit A/D (but ideally 24-bit A/D) and into a 16-bit session and also a 24-bit session. Tex, have you?
 
"Really?? No difference in sound even after putting down several tracks? What about like decays on, say, a sustained piano chord ringing out until the end, when it's really soft?"

I guess that was a pretty vague statement.

The tonal quality is the same. It's not like going from analog to digital or 8bit to 16bit. It's not that drastic. But the lower noise floor does give you the increased clarity on quiet parts that you mention and it's especially helpfull in large mixes.

I have been playing with a 24bit system for a few months now and the advantage of a lower noise floor can not be overstated. It is very forgiving if you track too low which is nice if you record yourself. You dont have to be so religous about getting such a hot signal and you can give yourself a little more 'headroom' while tracking without any noise penalty.
 
Ok, I'm no guru but let me take a shot at this.

The way I understand this is that aside from the extra dynamic range available due to the lower noise floor there should be another slight increase in headroom, this is how -

24 bit allows you more possible 'volume' values because it has more divisions, and they are in smaller increments.
For simplicity sake let's say 16 bit will allow 10 'steps', or volume values and 24 bit will allow 100 'steps'.
If you want to record a signal which has a volume of '9.1' a 16 bit system will record it as a value of '10' and you will get an 'over'. Whereas with a 24 bit recording it will register as '9.1' and not go 'over', you could even increase the recording level more up to '9.9' and still not get an over.
That is also the reason that the noise floor is lower, the minimum value that can be assigned to noise in a 10 step system is '1', but in a 100 step system a value of '0.1' is possible.
That of course is grossly oversimplified.


The way I understand bit depth and sample rate is as follows:

The bit depth is the accuracy with which the 'volume' or 'amplitude' of a sample can be measured.

On a one bit scale there are two possible values, one or zero - silence or full volume.
go to two bits and you can have four possible values - silence, 1/3 volume, 2/3 volume and full volume.

etc, etc.


The sample rate is how many times per second a measurement of volume is taken.

Picture it like a graph (or an audio editing window), the sample rate is how many divisions are on the horizontal axis and the bit depth is how many divisions are on the vertical axis.

The more divisions on both axis there are, the more accurately a 'picture' of the waveform can be reconstructed.
 
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