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dB and gain
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Peter said:
“but as a rule on any audio if youre driving audio so it hits into the red portion of any meter, you run a real risk of clippimng and distortion.”
>> The Sound Devices LEDS are red way before they go into distortion. My A/D converters show red 3 dB below clipping.
“digital is less forgiving, good, good, good massive distortion and no inbetween.”
>> Peter. I have tracks that have clipped on occasional peaks in Pro Tools and other software DAWs that sound fine.
Yes, analog VU meters with needles are too heavy (and therefore too slow) to catch peaks, but who uses them anymore anyway?
Regards,
Ty Ford
Want better production audio?: Ty Ford’s Audio Bootcamp Field GuideWatch Ty play guitar -
dB are maths. You can’t really understand what a decibel ever represents if you don’t understand the maths behind them. That explains why so many audio pros don’t really understand them either. A Bell is a logarithmic unit of measurement that expresses a unit’s value relative to a given baseline of the same unit. It’s not just for sound, and even for sound it applies differently wether you’re talking about sound propagation through air of electrical propagation through a conductor. It’s not meant to be easy.
You can work with dBs without understanding them, many do, but if you really want to understand the deciBell, it’s all about maths, formulas and numbers.
JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com -
Hi Jean-Christophe,
I’m terrible at math.
The thing ofcourse is that I’m working with audio, although I don’t understand the maths behind it.
But I’m thinking now…
If I don’t understand all of it, then they won’t understand it also.
So I’ll try to find a very neutral answer if someone asks this question to me again lol.
Something like “google it” or “search for it on Wikipedia”.
So I do understand there are different ways you can use dB, but it is not neccesary to know alle the maths behind it to be able to work with audio.
As I told before… I’m not an audio technician but meanly I use my ears when recording or editing audio.So I wanna thank all people here for there reply, because it made me a little wiser.
Greetzzzz
Fred
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The key to using dB as an effective reference is making it meaningful. When I simply say “6dB”, there is no indication of what I am talking about – am I talking about Sound Pressure Level (how “loud” something is) or am I referring to the difference in level between two audio clips as shown on the VU meters?
This is why there are various dB scales (dBu, dBV, dBSPL, dBFS, etc.). They allow us to refine what exactly we are talking about.
For example, one that may be particularly useful to you is dBFS (or Full Scale). Basically, this tells you how much headroom – in dB – you have left before clipping occurs. You can use if for any piece of equipment, per se, but it is normally seen when digital conversion/processing is employed. If an analog mixer can output a maximum of +22dBu, then THAT is its “0dBFS”. In order to keep short-duration signals from clipping the signal, it is best to have around 12dB-20dB of headroom. -18dBFS would indicate that you have 18dB of headroom before clipping will occur.
The dBu specification has a somewhat-interesting history involving the telephone company, but the spec itself can be used for comparing like pieces of gear and calibrating levels between them. (It is very helpful to know the math behind it, but that can be put on the back burner for now.) If you have a field mixer with a built-in tone generator, you can “send tone” so that your mixer’s levels match those of the recording device(s) down the line. This will ensure ample headroom so that your signal remains clean and clear.
I’m glad that you are looking into the resources you have been given. Please continue to ask questions here; we will be happy to answer them as we are able to. 🙂
Wolf
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“You have decibels (dB) used to measure sound.”
That is true for both physical (SPL = Sound Pressure Level) and electrical (voltage, power, etc.) measurements.
“0dB is the value that represents sound where an avarage person with normal hearing, hears nothing. In opposition where 110dB is a lot of sound that could cause hearing damage. So far so good.”
That is a generalization of how dB is used for SPL. Note that it has no direct correlation with how the term “dB” is used for electrical signals or for mixing, etc.
https://en.wikipedia.org/wiki/Decibel#Acoustics_2“In every respectable editing program you will find an audiomixer with UV meters. These UV meters are standard set to 0dB.
So, as far I’m with the program I assume this setting means that the imported audio is unchanged electronically meaning my sound will be imported with the same strength as it was recorded with my videocamera.”VU meters in the digital world are labeled “0dB” at the very top. That is known as dBFS (deciBels Full Scale) It means that “0dB” is all the bits on, the very maximum voltage you can possible handle. “When you’re out of bits, you’re out of beer” to paraphrase the old advert.
When we are “tracking” in a music studio or recording original dialog on a video/film set, we use some amount of “headroom” between our average recording peaks and 0dBFS. Because 0dBFS is the absolute maximum, there is no “grace area” (as there was back in the analog age). Some popular headroom offset values are -12dBFS or -20dBFS. The higher value (-12) is more commonly found in more casual, 16-bit production (as with semi-pro equipment, or for “run-n-gun” things like the evening news.) The -20 value is more commonly found in 24-bit sound recording for more formal and controlled productions like feature video/film production, etc.
“Not that my audio has 0dB if it would be measured with a audio meter.”
That is rather an ambiguous statement because several of the words (like “audio” and “measured”) have several different meanings in different contexts.“So I think to know that there’s dB to measure sound and there’s dB to measure the electrical current to change the strength of the audio wave, as wel..”
Yes, you are on the right track there. And there is also dB used other things, as well like measuring mixing ratios, gain, attenuation, etc.
dB is fundamentally a RATIO. It is not an absolute measurement like voltage or weight or height. It is use most commonly as a ratio when we talk about how much gain you need to boost microphone level up to line level (40-60dB). Or how much attenuation you might get through a long length of cable, or how much high-frequency reduction you would get from hanging thick curtains in your studio, etc.
When people use “db” as a MEASUREMENT, it is meaningless without a REFERENCE. Unfortunately, this reference is frequently omitted. For example, in modern digital use when you see the statement that something has “-10dB” output level, they are probably mean “dBV” where the zero reference point is 1 volt.
https://en.wikipedia.org/wiki/Decibel#Voltage
I didn’t know I was so popular. I am traveling in South Africa (a grueling location scouting trip for a large concert tour. It is definitely NOT a vacation.) Currently in CapeTown and back to Joberg this morning and then 30 hours back to home in Portland. NOT looking forward to that, either.
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“But I assume on the dB issue that I’m correct in saying that Sound in real live isn’t measured in the same way as used in a studio (or audio mixer)…”
It is not clear what you mean by that, but if you mean what I think you mean, then it is not a true statement. “Sound” (whatever you mean by that?) is measured the same way everywhere.
“…or as represented on a videocamera (gain, +3dB, 6dB, etc.)”
That is not a true statement, either. When we talk about gain it is exactly the same for any kind of electrical signal, whether it is audio or video or even RF.
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HI Ty
To address the points you raised 1 by 1.
I was really meaning the red or “danger” area in DAW / NLE meters, not field recorders etc, but i wasnt specific enough. Sorry.distortion.
i was reallly suggesting that digital doesnt have a saturation / steady onset of distortion in the same was as old analogue tape used to have. So when clipping occurrs, it is when all the digitas have become 1’s There is no more level available, and this usually represents itsself in my experience as a very noticable and objectionable crackke (mis spelt to beat profanity filter)Vu meters. Who uses them. Well apparently the original poster does in his NLE. That was where we started, and i googled the app and yes it seems to use VU. I agree theyre a wast of space.
Peter
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Hi Richard,
Tnx for this reply.
The big mistake I made was indeed assuming that dB was used in the same way as for example KG, or Volt or Watt and so on …
The only difference between me and the people who gave me the reaction that I was telling wrongfull things about dB was that the maths behind it are used different for different apllications, while they believe it is completely the same.
So to be honest I still don’t understand all of it.
But tnx to all of you guys I do have a better understanding now and it gives me a little more insight on how to use my audio and what my VU meters mean instead of simply avoiding going into red because that might cause clipping.
For example, when shooting video I mostly use 2 shotgun mics.
I have 2 XLR inputs on my camera and mostly I use them to generate a kind of stereo sound. (for theater and stuff, when I make shortfilm I use one mic, mostly on a boom)
Today I filmed an animator who brought a short (45minutes) show for kids, mostly for birthday parties, but today he hired an indoor location with the purpose of shooting the whole gig so we can make a promotional video.
Since there where 3 camera’s, I didn’t realy needed 2 mics, but I still used both of them.
I mostly don’t use AGC and set the gain equally for both mic’s.
Today I set one mic lower, and the ohter higher.
In the past it happened (with or without AGC) that I had clipping when the audience starts to applaud.
So I set one mic lower to avoid clipping when that happens.
The other mic was set higher so the animator was understandable.
(the animator had a headset mic that was send to speakers in the room)
So I imported the footage into Premiere and for the first time I was able to mix my audio in such a way that there was no clipping when loud but the artist was clearly understandable all the time.
I don’t know if that’s te good way to go about it.
But after reading all your reply’s, read your links, did some googeling and Youtubing, this was what I came up with in an attempt to improve my skills as an amateurfilmer.And so far (at least today) it worked great.
So, tnx again.
Greetzzzz,
Fred
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Freddy, and Peter,
What DAW has analog meters?!
Regards,
Ty Ford
Want better production audio?: Ty Ford’s Audio Bootcamp Field GuideWatch Ty play guitar -
That I don’t know.
I even had to google te word DAW lol.
Anyway, I don’t have equipment with analog meters.greetzzzz,
Fred
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