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Author Topic: Measure max\average amplitude?  (Read 6716 times)

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Offline StarkRavingCalm

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Re: Measure max\average amplitude?
« Reply #15 on: April 27, 2015, 03:42:47 PM »
You don't need to leave the dc offset in...  I'd argue for removing it, though have no idea how to do that with command line programs.

I didnt use sox to increase the amplitude.
Different program.

Offline bombdiggity

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Re: Measure max\average amplitude?
« Reply #16 on: April 27, 2015, 05:50:26 PM »
^ You should be able to remove the dc offset.  In audition it's called "center wave" under amplify/fade (process)

While the discussion is still open...

Most people like to record around -12db, is it safe to say most people like to master at 0db?

Also I think this was answered but just as you wouldn't record to 0db you shouldn't master to it.  You can come as close as you want while leaving a little room though.  How you get there will impact the sound though.  Sometimes trial and error but with a dynamic live recording a bit of limiting or compression usually gets you a more even listen and more solid output.  Too much will sound forced though.  Loud rock shows usually have that built into the mix so you can often just amplify. 
Gear:
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Nak CM-100/CM-300 w/ CP-1's or CP-4's
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>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline dabbler

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Re: Measure max\average amplitude?
« Reply #17 on: April 27, 2015, 07:19:45 PM »
sox has a "dcshift" effect to remove DC offset, however AFAIK it only works if DC offset is constant throughout the file.  Alternatively (as noted in the sox manpage), you can also use a highpass filter at a low frequency such as 10 or 15Hz to remove the offset (while introducing a short phase delay).

I usually highpass at 15Hz myself (and often higher depending on the material)

Offline rocksuitcase

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Re: Measure max\average amplitude?
« Reply #18 on: April 27, 2015, 08:23:10 PM »
bump to learn things >:D
I am so old skool I still use Wavelab's Global analysis tool ,and then adjust overall gain that way. My preference is to never master above -.5. lately on my PMD661 I've been recording around -12 to -8 avg, but find when I get it on the computer, there is some peak which goes to -4 or so.
Obviously I am NOT the person to answer your question, but i like learning what other people use.
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Offline StarkRavingCalm

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Re: Measure max\average amplitude?
« Reply #19 on: April 29, 2015, 11:03:40 AM »
I am using MPowered ProTools. Mainly, because I like the vertical slides.
I have the source in one 'channel' and I create a Master Fader.
In the example above, I increase the source channel by 12db (this is max) and I leave the MF at 0db.
Depending on the source I may need to set MF to +2db or such so that the final mix is about 0db (or -2db for headroom) but that is for another day.

My question now refers to dithering.
I don't want to go too far with that topic as I have a decent understanding of it.
My questions are:

Do you only need to dither IF you are down-sampling? (i.e.. 24/28 > 16/44)

At what point in the process do you dither?
Pre-Mix? Or when finalizing?
Or if you have already finalized at 24/48 and want to convert your file to a 16/44 version?

Offline bombdiggity

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Re: Measure max\average amplitude?
« Reply #20 on: April 29, 2015, 02:07:03 PM »

At what point in the process do you dither?
Pre-Mix? Or when finalizing?
Or if you have already finalized at 24/48 and want to convert your file to a 16/44 version?


Always last.  You want to make any editorial changes to the files at the original rate. 
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline Gutbucket

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Re: Measure max\average amplitude?
« Reply #21 on: April 29, 2015, 03:03:40 PM »
Apply dither immediately prior to truncating excess bits, anytime you truncate.  That means whenever going from a higher bit-depth file to a lower bit-depth one.  Typically that's done when saving your 24bit source (or whatever internal rate the software is using, which is probably higher than that, regardless of the bit-depth of your source files) as 16bit final output files.  Most software will dither and truncate for you in one step, automatically.  IMHO, you needn't worry too much about the type of dither and if it's "noise-shaped" or not, especially with live music which you have level adjusted so that the peaks are at a decently high level.  In that case the dither will be so low in level it will be completely burred beneath the much higher noise-floor of your recording so you'll never hear it.  Basic "triangular" dither is fine.

This is not the same as down-sampling however, often done at the same time.  That's a different process which converts from one sample-rate to another. Typically converting a 48kHz or 96kHz file to 44.1Khz.  That's a more calculation intense type of conversion, and any artifacts from that conversion can potentially manifest throughout the entire frequency range rather than only effecting the very quietest portions.  For that reason, I suspect using higher quality re-sampling routine may be more important than using fancy dither, as long as your machine can handle the processing load.
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Offline StarkRavingCalm

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Re: Measure max\average amplitude?
« Reply #22 on: July 17, 2015, 02:11:43 PM »
Ok, so I have a few more questions.

It's either my poor math skills, or me not understanding Master Fader, or something else...


(hypothetical)
So I have a file that has been imported into a audio project
Say it is:
      Overall     Left      Right
Pk lev dB       -12.50      -12.50    -12.50


I raise "channel 1/2" to 12.0 db (the max)
I then set my MF to -1.5db

Shouldnt my resulting file be -2.00 db?


How is it calculated if there is say, "channel 3/4" and/or "channel 5/6"?



Basically, my "mix and master method" is:

Bring SBD to 0db
Bring AUD mics up to where I like the sound
Mix them down into one file where the resulting file is -2db (mainly to give headroom)

Or if straight AUD:

Bring AUD to 0db
Mix it down into one file where the resulting file is -2db (mainly to give headroom)

Offline bombdiggity

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Re: Measure max\average amplitude?
« Reply #23 on: July 17, 2015, 02:33:05 PM »
Ok, so I have a few more questions.

It's either my poor math skills, or me not understanding Master Fader, or something else...


(hypothetical)
So I have a file that has been imported into a audio project
Say it is:
      Overall     Left      Right
Pk lev dB       -12.50      -12.50    -12.50


I raise "channel 1/2" to 12.0 db (the max)
I then set my MF to -1.5db

Shouldnt my resulting file be -2.00 db?


How is it calculated if there is say, "channel 3/4" and/or "channel 5/6"?


I suspect your MF overides the individual channel applications, so if MF is set to max -1.5 then -1.5 is what you get regardless of what else you did at the same time (or prior to it). 

Basically, my "mix and master method" is:

Bring SBD to 0db
Bring AUD mics up to where I like the sound
Mix them down into one file where the resulting file is -2db (mainly to give headroom)

Or if straight AUD:

Bring AUD to 0db
Mix it down into one file where the resulting file is -2db (mainly to give headroom)

There's no reason to leave -2db "headroom" in mastering if the final output is really -2db.  You need some headroom for recording since you can't fully predict the ultimate levels in an evolving live performance.  Once it's all committed to a recording there's no reason for headroom anymore.  You don't want to to all the way to 0 since that is the clip point but you are fine going to -.25 or -.2 or -.1.  I usually master to -.1. 

Limiting to -2 leaves basically 2 db of potential range completely unused.  2db you will hear as significantly quieter, though the difference between .2db and 0db isn't really noticeable. 
« Last Edit: July 17, 2015, 02:35:42 PM by bombdiggity »
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline StarkRavingCalm

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Re: Measure max\average amplitude?
« Reply #24 on: July 17, 2015, 03:29:38 PM »
Ok, so I can adjust to .2db

But I am still a little confused as the role MF plays as it doesnt always seem to limit the levels.
In other words, my resulting files are not always equal to what the MF is set at.

Offline Gutbucket

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Re: Measure max\average amplitude?
« Reply #25 on: July 17, 2015, 03:41:09 PM »
The -1.5dB indication on the masterbus fader is the gain applied at that point- which is simply a relative measure of the gain change it is providing at that stage.  Since the program is operating internally with floating-point math, that relative level change may or may not be appropriate for preventing overs in the fixed, lower bit-depth file output.

Process depends somewhat on the software you are using.  Most modern Digital Audio Workstation software works with floating-point mathmatics, which means you typically needn't worry about internal headroom or clipping within the software, only on it's way in or out of the DAW.  Typically you will have control over the signal level of each individual mono channel or stereo channel as well as separate level control over the 2-channel mix bus (maybe called the master bus).  Since the program itself is working internally with higher floating-point bit-depth math, you don't really need to normalize the individual parts to be mixed, although doing so may can help manage things for you.  What is more important is making sure that the final output level from the master bus is the correct level- not to high, not to low, but just right Goldilocks. 

Basically, my "mix and master method" is:

Bring SBD to 0db
Bring AUD mics up to where I like the sound
Mix them down into one file where the resulting file is -2db (mainly to give headroom)

Or if straight AUD:

Bring AUD to 0db
Mix it down into one file where the resulting file is -2db (mainly to give headroom)

Just a reminder that the most appropriate "mix and master method" depends on the qualities of both your AUD source and SBD source.  With a really good AUD, you'll probably do best with a lot more AUD than SBD in your matrix.  Usually some SBD will be beneficial for even a fantastic AUD, but with a really good AUD often very little SBD is necessary- just enough to bring up whatever elements may be a bit low in the AUD, and to crisp-up vocal clarity and transients and bring those elements forward a bit to make then more immediate and engaging rather than soft and distant sounding.  That's favoring the stew to taste by adding enough SBD spice to the base stock AUD.

If the SBD is better than the AUD then doing it other way around lie you mention may be more more appropriate- adding just enough AUD to bring the dry but better sounding SBD to life, with the AUD's room and audience contribution rounding things out.  In that case you're adding enough AUD spice to the SBD base stock to taste.

So, no hard rule concerning which component should be higher in level or normalized first, play that part by ear.  Just check to make sure that the final output bus level is where you want it before writing the output files.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline StarkRavingCalm

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Re: Measure max\average amplitude?
« Reply #26 on: July 17, 2015, 04:49:56 PM »
Understood.


So I guess it's me not understanding the math of how we end up at a certain db level, especially when I am running 4 or 6 channels and a MF as well.

Offline Gutbucket

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Re: Measure max\average amplitude?
« Reply #27 on: July 17, 2015, 05:34:59 PM »
You should to check the level out of the master in an absolute sense, relative to 0dbfs (indicated via the master buss meters, and/or 'over' indicators). 

The levels up to that point within the mixing software are all relative to each other.  That includes the gain applied by of the master fader.  The output gain indicated by the fader position (or any numeric indication of the fader gain) is relative to the input level of signal to that fader, not relative to 0dBfs which is absolute.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline morst

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Re: Measure max\average amplitude?
« Reply #28 on: July 27, 2015, 06:00:50 PM »
So I guess it's me not understanding the math of how we end up at a certain db level, especially when I am running 4 or 6 channels and a MF as well.
I hope the following addresses the question: Please if someone could confirm my math- my impression is that summing two identical signals together will increase their peaks by +3 dB. Adding four together would increase peaks by +6dB.

So if you have a two-source mix that peaks at -3dB on each source, they should add up to approximately no more than -0dB when the peaks line up, and lower in all other spots. If you had two source recordings that peaked at -0dB, you could set each of them to -3dB and theoretically avoid any "overlevel" samples. Likewise (I think) you can take 4 channels at -0dB, and set each of their faders to -6dB and your output should wind up under -0dB.

Now, if you add a fudge factor of a .1dB, and drop two sources, say, -3.1dB, then I think they should peak out at -0.1dB for the sum.

Other things to note are that if the peaks don't line up perfectly (since we have two very different sources, SBD & AUD, right?) then you might be able to run all sources at -0dB (full scale) and they won't peak higher than -0.0dB anyhow!? I've seen it happen!
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