understanding peak-meters

[whomper]

are we talking instantaneous peak
recent peak
or entire track peak ?

we really need the entire track to avoid clipping.
and we cant know that until after we are done.

while there may be a small time delta where one side of the
wave is larger/smaller than the other, on the average they better
be symmetrical over all or there will be a dc offset.

a priori before knowing the max peak we need to record at
a level that is below the maximum anticipated PLUS leave an
additional margin in case we guess wrong.

my margin, as in at least one international standard is -24.
other standards use -18dBFS

feel free to go as high as you like
as long as you are prepared to go lower when you discover
that you clipped at that level

noobs complaining on bbs forums about problems usually
set their level way too high -- often -6 to even 0

[billw58]

while there may be a small time delta where one side of the
wave is larger/smaller than the other, on the average they better
be symmetrical over all or there will be a dc offset.

Try generating the wave I specified in my previous post. It has no DC offset but is asymmetrical. The light blue wave area is pretty much symmetrical, but the peaks are not. Run the Normalize effect with Remove DC offset checked and Normalize unchecked and it does nothing.

my margin, as in at least one international standard is -24.
other standards use -18dBFS

I believe those are transmission standards, leaving adequate headroom for unexpected peaks.

noobs complaining on bbs forums about problems usually
set their level way too high -- often -6 to even 0

I guess I'm a noob, because when transcribing LPs, I use -6 dB for my setting on the loudest part of the LP. Ticks and pops may clip, but who cares?

Live recording is another matter. I've found that -12 dB is usually adequate. But again you have to set your levels during the loudest expected passage.

-- Bill

[billw58]

Screenshots of the wave generated acc/to my previous recipe - possible good for testing any peak meter response.

asymmetricWave1.png (14.15 KiB) Viewed 2128 times

asymmetricWave2.png (17.06 KiB) Viewed 2128 times

In the .aup file we find:

<simpleblockfile filename="e00005ba.au" len="262144" min="-0.584424" max="0.995365" rms="0.406524"/>

-- Bill

[whomper]

my margin, as in at least one international standard is -24.
other standards use -18dBFS

I believe those are transmission standards, leaving adequate headroom for unexpected peaks.
...

Live recording is another matter. I've found that -12 dB is usually adequate. But again you have to set your levels during the loudest expected passage.

I have no idea what the loudest will be for either live or pre-recorded material.

With some estimates of maximum possible SPL/voltage which would cap the peaks, -24 seems reasonable to use for recording.

Make it as loud as I like when I have finished tracking mixing & mastering. But why risk clipping in the chain ahead of the output?

[steve]

when transcribing LPs, I use -6 dB for my setting on the loudest part of the LP. Ticks and pops may clip, but who cares?

Live recording is another matter. I've found that -12 dB is usually adequate. But again you have to set your levels during the loudest expected passage.

I quite agree, though if recording unpredictable sound sources (such as very young children) it may be necessary to allow even more headroom (there's a huge difference in level between a small child burbling and a small child squealing with excitement
However it is also important to be aware that allowing more headroom than is necessary will result in the background noise level to be louder than necessary by an equal degree. So as you say, for best results "set your levels during the loudest expected passage" (including a safety margin just in case).

[Gale Andrews]

Confirmed on 1.3.13 Nov 7. It's also fairly easy to generate an asymmetrical wave. Generate tone into three separate mono tracks: 220, 440 and 880 Hz at level 0.2. Slide the 440 and 880 Hz tracks so the first peak lines up with the first peak in the 220 Hz track. Mix and Render.

-- Bill

I'm not sure if you know, but a fix has been committed for this - see bug 259. The fix is in the Win Unicode Nightly, but not yet in the Mac Nightly (will be in the next one after 24 Nov 03:15).

Fix seems to be OK so far on Windows and Linux (reads correct levels also).



Gale

[whomper]

quote ...
This will generate a sine tone that is offset so that it is all in the range of 0 to +1
When you play this track, as expected the peak level is immediately shown in dark green as 0dB and the RMS value (shown in light green) climbs up to -4.3dB
---------------
I would expect the peak to be -6
and a square wave to be at 0dB
and the rms to be -3

clearly I am missing something
(perhaps believing too much of what I read)

on the other hand
there are several standards for measuring peak/rms etc
that give different values for the same signal depending on the method you choose

and some DAWs implement the measurements wrongly to boot

[steve]

I'm not sure if you know, but a fix has been committed for this - see bug 259.

Excellent. I've just tried it and it correctly indicates the absolute value of the signal with the dark coloured meter bar, which is in agreement with common practice, (and with the description in Wikipedia. http://en.wikipedia.org/wiki/Amplitude#Peak_amplitude )

[whomper]

so is the wikipedia article wrong when it says

Since a peak measurement is not useful for qualifying the noise performance of a system, or measuring the loudness of an audio recording, for instance, RMS measurements are often used instead.

There is a potential for ambiguity when assigning a level on the dBFS scale to a waveform rather than to a specific amplitude, since some choose the reference level so that RMS and peak measurements of a sine wave produce the same number, while others want the RMS and peak values of a square wave to be equal, as they are in typical analog measurements.[3][4][5][6]

* For the case in which the RMS value of a full-scale square wave is designated 0 dBFS, all possible dBFS measurements are negative numbers. A sine wave could not exist at a larger RMS value than −3 dBFS without clipping, by this convention.[7] This is the convention used in Euphonix meters.[8]
* For the case in which the RMS value of a full-scale sine wave is designated 0 dBFS, a full-scale square wave would be at +3 dBFS.[9][10] This is the definition specified in AES Standard AES17-1998[11] and used in Dorrough meters.[8]