Skip to main content
Topic: 16 bit, 24 bit and Noise Floor (Read 19954 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Re: 16 bit, 24 bit and Noise Floor

Reply #50
I'm suggesting that with a recording environment that yields a noise floor of -60dbfs it makes no difference at whether you capture in 16 bit or 24 bit as you effectively only have 10 bits to work with and so any theoretical benefits of using 24 bit are lost
i am posting a reply since I found this post helpful
If my only purpose is to record spoken word and the dynamic range of my speech comes around 40dB, All i need is probably 12 bits
giving a 10dB headroom and minimum 10dB noise floor clearance with my signal peaking at -10dB dbfs. I believe this is similar to the situation what is stated here in the original post since I do it in a room where the noise is peaking at around -60dB. For me I believe there wont be any sort of advantage in using a 24 bit recording interface.
Also from what I understand the 24 bit recording and 16 bit recording uses same number of bits to record a 40dB dynamic range speech like mine, so there is no high definition there of any sort contrary to the popular perception of absolute beginners  like me.

Correct me if I am wrong please.

MOD Edit: Add proper quote tags

Re: 16 bit, 24 bit and Noise Floor

Reply #51
16 bits will be probably enough, especially if you don't want to do any further processing, but the reasoning isn't completely correct.

Quantization always adds some noise (unless the source is already quantized to the same or lower bit depth), it's just a question at which point it becomes insignificant for your use case.

Quote
I do it in a room where the noise is peaking at around -60dB

Comparing noises by peak levels won't give a good guidance, the interesting metric here is not peak levels, but the perceived loudness.
Quantization noise has constant loudness, so it'll likely have a smaller difference between peak level vs average perceived loudness. The frequency characteristics of noises are also important to determine if one noise will be completely masked by other noise.

Quote
Also from what I understand the 24 bit recording and 16 bit recording uses same number of bits to record a 40dB dynamic range speech like mine

PCM coding doesn't work like this. All bits are used all the time. Perhaps you can elaborate, what do you mean by "use same number of bits"?
some ANC'd headphones + AutoEq-based impulse + Meier Crossfeed (30%)

Re: 16 bit, 24 bit and Noise Floor

Reply #52
If we're talking noise floor from analog equipment, that is quite different than noise from lower-resolution quantization. Analog noise doesn't clip information digitally, and thus can be removed with good noise cancellation.

Re: 16 bit, 24 bit and Noise Floor

Reply #53
@ajp9 What does it mean - "clip information digitally"?
some ANC'd headphones + AutoEq-based impulse + Meier Crossfeed (30%)

Re: 16 bit, 24 bit and Noise Floor

Reply #54
If we're talking noise floor from analog equipment, that is quite different than noise from lower-resolution quantization. Analog noise doesn't clip information digitally, and thus can be removed with good noise cancellation.
Not if dithering is involved, and it always is.  Once an ADC is dithered the resulting quantization noise is very similar to analog noise, differing in spectrum only.

Re: 16 bit, 24 bit and Noise Floor

Reply #55

Quantization always adds some noise (unless the source is already quantized to the same or lower bit depth), it's just a question at which point it becomes insignificant for your use case.



I use a 16-bit interface for this recording. I do the post processing in Audacity in 32 bit float format and I export it as mp3.

I use a Noise Gate and remove all the part below -50dbFS threshold.
So all parts of the recording below this level I am considering as undesirable. This is what I wrongly attributed to needing lesser number of bits.
I think I  can rephrase it as the part of the signal those extra bits in 24-bit capture, are useless to me since I think its just my room noise.

I am not sure if I should be worried about the quantization noise in this situation?

Quote
PCM coding doesn't work like this. All bits are used all the time. Perhaps you can elaborate, what do you mean by "use same number of bits"?

Yes I got your point, it was my misunderstanding.Sorry.

Re: 16 bit, 24 bit and Noise Floor

Reply #56
> I am not sure if I should be worried about the quantization noise in this situation?

To say for sure, you'd need to compare and decide. But if you simply remove the quietest parts, I think it's most likely not worth buying another soundcard for this.
some ANC'd headphones + AutoEq-based impulse + Meier Crossfeed (30%)

Re: 16 bit, 24 bit and Noise Floor

Reply #57
> I am not sure if I should be worried about the quantization noise in this situation?

To say for sure, you'd need to compare and decide. But if you simply remove the quietest parts, I think it's most likely not worth buying another soundcard for this.

Yes thanks, I tried out most of the tests mentioned in this post. I understood that its not exactly intuitive and its not good to make assumptions and  I think i have an idea of what the difference might be.
But like you said to know it for sure the difference, I will need a 24 bit interface and test 16-bit mode and 24 bit mode and compare the output.
I tested the 8-bit and 16-bit recordings for spoken words and there is a perceivable difference in terms of noise. But I understand that the audible  difference won't be so stark between 16 -bit and 24- bit.
So my conclusion is I don't need to buy another sound card only for the sake of a 24 bit depth, for my purpose.
This has been very helpful. thanks so much






Re: 16 bit, 24 bit and Noise Floor

Reply #58
Quote
I think i have an idea of what the difference might be.
But like you said to know it for sure the difference, I will need a 24 bit interface and test 16-bit mode and 24 bit mode and compare the output.
I tested the 8-bit and 16-bit recordings for spoken words and there is a perceivable difference in terms of noise. But I understand that the audible  difference won't be so stark between 16 -bit and 24- bit.
So my conclusion is I don't need to buy another sound card only for the sake of a 24 bit depth, for my purpose.
This has been very helpful. thanks so much
Right!   At 16-bits you can't hear quantization noise under any normal-reasonable conditions.   

As you may have noticed with your 8-bit experiment, quantization noise is different from regular analog noise.     Analog noise exists constantly in the background.   

Quantization noise rides on top of the signal and when there is digital silence there is no quantization noise (something like a noise gate).    But like analog noise, it's most noticeable with a quiet signal and may be masked (drowned-out) with a higher signal.

Re: 16 bit, 24 bit and Noise Floor

Reply #59

As you may have noticed with your 8-bit experiment, quantization noise is different from regular analog noise.     Analog noise exists constantly in the background. 
Quantization noise rides on top of the signal and when there is digital silence there is no quantization noise (something like a noise gate).    But like analog noise, it's most noticeable with a quiet signal and may be masked (drowned-out) with a higher signal.
 

This is interesting. Yes indeed I noticed that I cannot remove the noise in 8 bit using noise gate since it seem to be riding on top of my actual desired audio where as the background noise was completely removed adjusting a noise gate threshold.This also removed the quantization noise in the silent part since the whole signal during silent part were removed I presume. But whenever the words were spoken I could hear the noise. With dithering applied during export also this noise was audible.

For original 16 bit recording this noise is not much distinguishable.With noise gate it sounds very clean.  I presume 24 bit does improve on the 'noise riding above the signals', but the difference will be hard to perceive under normal conditions.

This interests me in another question if I may. Where does the SNR of the microphone I use, fit in in this whole scenario?
I use a Shure SM48. The audio interface I use has a SNR  specification of 85 dB. The room I record in the noise peaks around
-65dbFS.( I know this is not apt,but I am yet to figure out how to do a spectral analysis of the noise.)
thanks







Re: 16 bit, 24 bit and Noise Floor

Reply #60
@ajp9 What does it mean - "clip information digitally"?
When binary bits are removed (clipped off) to fit a smaller significant digit resolution. Information is necessarily lost that can't be recovered.

The clear advantage of digital encoding is its ability to reproduce exact copies, but any digital conversion, not just A/D, will lose information to some degree, so accuracy needs to be high to lose the least. Depth is unavoidably part of that accuracy.

Dithering when decimating helps encode signal energy because it takes more than one sample to make a wave, but it's a limited fallback, and not always guaranteed to be accurate. Only randomized dithering works well with audio signals because ordered dithering or delta-sigma modulation can combine with similar signals to produce interference patterns—something where a lowpass would help but a lowpass could interfere with the purpose of encoding for a high bandwidth.

Once an ADC is dithered the resulting quantization noise is very similar to analog noise, differing in spectrum only.
Similar, but not the same. Dithering—especially noise-shaped dithering—can help improve clarity or SNR in more audible parts of the spectrum. But digital decimation always removes information in ways that analog cannot.

Think of how digital information is recorded, overwriting some other bits on a storage medium; that's as good as it gets; there's no more information for that recording itself; you can't pull other layers the way you can restore from tape. That isn't to say analog media can always be recovered, but with more advanced noise prediction/cancellation you could recover information that was previously thought unrecoverable. Digital may add additional security that the FBI can't restore what you decimated or overwrote, but neither can you if you don't have a more accurate copy.

What I'm saying may sound trivial, but the most important content ought to be recorded at a higher resolution if you can afford it to preserve history.

At 16-bits you can't hear quantization noise under any normal-reasonable conditions.
16 bits is generally adequate for masters because there's a point where the brain stops caring beyond a certain signal threshold (apart from overall amplitude). For sight, it was measured that humans can't see more than just over 600 levels per stepping. Even the best ears on HA can't ABX LossyWAV from the original, and that's limiting significant digit precision to 8 bits on a floating scale (upper/lower bound of 16 bits).

Re: 16 bit, 24 bit and Noise Floor

Reply #61
Quote
I use a Shure SM48. The audio interface I use has a SNR  specification of 85 dB.
That's tricky because you have to make assumptions about the signal.   Speaking/singing louder, or getting closer to the mic, or using a more sensitive mic will increase the signal which improves the signal-to-noise ratio.   A directional mic (such as the SM48) also helps the SNR because the signal comes from one direction and the room noise comes from all directions.    (A more sensitive mic will help with the electrical preamp noise but of course it doesn't improve the acoustic SNR.)    A weaker signal will make the SNR worse.

If you have a USB-powered interface, sometimes noise gets-in through the USB power and the interface might not actually meet it's published specs.

Quote
The room I record in the noise peaks around -65dbFS.
If you are getting a "good signal" that beats the audiobook spec of -60dB and that's very good for home recording!   But if you have to amplify, the noise will be amplified too.


Re: 16 bit, 24 bit and Noise Floor

Reply #62
  A directional mic (such as the SM48) also helps the SNR because the signal comes from one direction and the room noise comes from all directions.    (A more sensitive mic will help with the electrical preamp noise but of course it doesn't improve the acoustic SNR.)    A weaker signal will make the SNR worse.
Yes , the dynamic mic of around 150 ohm has self noise much lesser than the preamp noise created while amplifying  its signal.

Discarding the background noise amplification and taking into consideration only the preamp noise ,hypothetically speaking if my 16 bit interface noise floor is 85db(got this value from an online review of the model)
and the mic preamp inside the same interface is producing a noise around 16db to drive the dynamic mic, will my effective noisefloor of the interface be at 69db now instead of the 85db?

Quote
If you are getting a "good signal" that beats the audiobook spec of -60dB and that's very good for home recording!   But if you have to amplify, the noise will be amplified too.

Yes, noted. Tell me if I am wrong , If a 85db SPL system plays the dialogues mixed at -10dbFS the loudness will will 75db SPL
and if I have a SNR of 60db, the noise will be played at a loudness of 15db SPL which will go below the noise floor of even a quiet room and will be inaudible.

thanks



Re: 16 bit, 24 bit and Noise Floor

Reply #63
Quote
Yes, noted. Tell me if I am wrong , If a 85db SPL system plays the dialogues mixed at -10dbFS the loudness will will 75db SPL
dB SPL and dB FS are almost never calibrated so let's forget about "FS" for the moment.   But they are correlated, so if you are playing a file at 85dB SPL and you reduce the digital level by -10dB, the analog also gets reduced by 10dB and you'll get 75dB SPL, and any noise in recording will also be reduced by 10dB.    (There still may be some more-constant noise from the analog side of the playback system, but that's another topic.)

Quote
and if I have a SNR of 60db, the noise will be played at a loudness of 15db SPL which will go below the noise floor of even a quiet room and will be inaudible.
Basically, yes.    If the SNR is 60dB and the SPL is 85dB you won't hear the 15dB SPL noise.


Re: 16 bit, 24 bit and Noise Floor

Reply #64
Thanks

Re: 16 bit, 24 bit and Noise Floor

Reply #65
This gives a totally different picture about the noise floor.
http://www.avisoft.com/tutorials/understanding-microphone-and-recorder-preamplifier-noise-specifications

"The specifications provided by the recorder manufacturers are often difficult to interpret. Due to marketing considerations, many manufacturers tend to publish large dynamic range numbers (e.g. > 100 dB) that are only valid for high-level signals.

For instance, the microphone input of the Marantz PMD671 .(SNR IEC-A weighted : LINE 92db ,MIC 65db) is honestly specified with a “poor” signal-to-noise ratio of 65dB(A), while the M-Audio MicroTrack claims a dynamic range of 100dB(A)

The overall inherent noise floor of the entire recording system results from the combination of the inherent noise floors of both the microphone and the recorder. It is important to note that both noise components add geometrically (RMS)

 it turns out that the optionally available 24 bit recording format cannot provide any significant improvement of the noise performance."

Re: 16 bit, 24 bit and Noise Floor

Reply #66
Quote
The specifications provided by the recorder manufacturers are often difficult to interpret. Due to marketing considerations, many manufacturers tend to publish large dynamic range numbers (e.g. > 100 dB) that are only valid for high-level signals.
Re-phrasing an old saying, "There lies, damn lies, and specifications".  :D

Quote
The overall inherent noise floor of the entire recording system results from the combination of the inherent noise floors of both the microphone and the recorder. It is important to note that both noise components add geometrically (RMS)
Plus the acoustic noise.  ;)

Quote
it turns out that the optionally available 24 bit recording format cannot provide any significant improvement of the noise performance.
Pros often record at around -18dB (for some strange "traditional" reasons or maybe to allow extra headroom).   At -18dB you are "loosing" 3-bits so at those levels maybe you can argue for 24-bits.   But, when you mix you are adding bits (mixing is literally done by summation) so if you are multitracking it's less important.

From what I've read most 24-bit ADCs & DACs are only accurate to about 20 bits, but that shouldn't affect the noise floor or anything we're talking about here.

Re: 16 bit, 24 bit and Noise Floor

Reply #67
Pros often record at around -18dB (for some strange "traditional" reasons or maybe to allow extra headroom).  
The -18dB figure comes from the need to calibrate a VU meter (which is a special case, averaging meter, 300ms integration time) to a true peak meter (instantaneous) found on a digital recorder, calibrated in dBFS.  When you put up a tone at 0VU, you can calibrate that tone anywhere on the dBFS meter.  -18dBFS is a compromise, allowing good headroom for true peaks that won't be metered correctly but the slow VU meter and provide headroom for unexpected loud peaks.  A rule-of-thumb true-peak to VU differential is 8 to 10dB.  It's not unusual to "peg" a VU meter during a very loud passage, so between 15 and 20dB of calibration offset is what's required to avoid clipping at 0dBFS.

In the early days of the CD, replication labs specified that there could be no peaks at 0dB(FS) (the FS term was a late addition).  And since adjusting a digital signal in post was a bit difficult initially, we had to be careful, especially if not using any dynamics processing.  Hence, there were several 0VU calibrations: -15dBFS, -18dBFS and -20dBFS. 
At -18dB you are "loosing" 3-bits so at those levels maybe you can argue for 24-bits. 
Bits are never lost, they're just not active.  You don''t loose 3 bits, they're there for a purpose, even if it's for that one peak in the entire record that hits 0dBFS. 
But, when you mix you are adding bits (mixing is literally done by summation) so if you are multitracking it's less important.
You aren't adding bits, the bits are always there.  When you mix the final result still has to fit below 0dBFS on the highest peak.  Mixing is a sum, but that sum is scaled by the mixer, or we'd have to establish a new reference 3dB down every time we added a channel.  Even if bits are inactive for most of the recording, an even if the recording never exercises all bits at once, the inactive ones serve a purpose: headroom, a place-holder in case you need it.   Analog is no different, BTW, we have all the same issues and surprisingly, at the same levels.   Only the metering references change.  We generally don't worry about frequent peaks falling a few dB short of clipping our summing amp, do we?  Are we losing dynamic range doing that because we aren't using up all the analog headroom?  No, because the DR is limited already elsewhere in the chain, at the low level end by microphone self noise, preamp noise, and the big one, room noise.  Hopefully the summing amp is one of the quieter amps in the system.
From what I've read most 24-bit ADCs & DACs are only accurate to about 20 bits, but that shouldn't affect the noise floor or anything we're talking about here.
Almost.  Most 24 bit ADCs have 20 bit noise performance.  When you try to build an ADC that has its own internal noise floor somewhere around the 24 bit level, you run headlong into problems with thermal noise.  Heck, the 20kHz Johnson noise of a 2000 ohm resistor is only -122dBV, so you have to jump through some pretty big hoops to get real 24 bit performance.  I know of only one company that marketed such an ADC, and they cascaded more than on ADC to get it to work.  Everything else has about 20 bit noise floor.  That's not the same as "accuracy", of course, which isn't measured in bit count.

 
SimplePortal 1.0.0 RC1 © 2008-2020