Audio level not calibrated?

About the measurement of loudness here a detailed explanation.|en)

Here is also an explanation about the true peak level:

On “Peak program meter” a detailed explanation affects a large number of references and existing standards:

According to all this, the measurement of loudness (especially watching the true peak TP) seems a wise way to avoid unwanted peaks and distortions when converting digital audio to analog.
In the loudness measurements that I did with the Youlean Loudness Meter 2 plugin (in my first response), red marks are observed that indicate a true peak value above 0 dB (+0.5 dB).
However, the TP value in the loudness meter in Shotcut marks a positive value (728.5 dBTP) out of scale range (-50 to +3).
I should ask about this.
Finally I overcomplicated the answer to your problem.:pensive:
Searching the forum, I found this.
I hope it helps.

Nice posts @ejmillan
Agreed that there is a bewildering number of standards and measuring methods.
I always work with the EBU R128 specs and have found SC to be pretty much spot on.

Often prepare short intros or promos for broadcast using SC and it has never let me down.
For quick jobs, find SC easier to use than Resolve or Premier.

However, something does not fit.I do not understand the TP value of the loudness meter in SC.
Does not match the values of other VST meters (EBU R128).
I put my question in this thread: Doubts about the TP value in the loudness meter

I found a free VST plugin to measure loudness in Audacity.
You can measure in RMS or EBU (LUFS).

I used the previous version (dpmeter3) and it worked well in Audacity.
This meter has many measurement modes.
Incorporates among others: RMS (factory default), LUFS EBU R128, DB K-20, etc.

I have not tried it, but I think it also allows you to apply a gain to the audio source from the same plugin.
Version 4 of this plugin, also works in Audacity.

OK, problem solved. All this was due to the version of Shotcut I was using (17.06.02 in the Debian Stretch release). With this version, when moving the video clip to the timeline, the audio level drops significantly: -13,5dB with the video I was working on (voice audio track) and -6dB with a pure 1kHz tone. This is no more the case in the latest Shotcut release (19.02.28) so I consider that this problem has been addressed and fixed. There is still a difference between the audio level of the video track and the level reported by the peak meter: I recorded a video with a 1kHz tone at 0dB and when played in Shotcut the peak meter shows apprx. +2dB. This is apparently due to oversampling (see this old topic: Shotcut peak meter reads incorrectly - lowers volume while rendering). Thank you all for helping me solve this and sorry for having put up a problem which no longer exists.

I apply a 1 kHz tone with 0dBu voltage level at the input of my capture card then extract the audio from the video and open it in Audacity. Audacity shows 0dB max for the file (or +1 level).

Still to be clarified is what exactly the peak meter displays in a frame. Have a look at this screenshot where you can see the audio in a frame. The audio is a 1kHz tone slightly peaking at -1db in Audacity, AM modulated at 99% with a square wave at apprx 50Hz. So what value does the peak meter show in the following screenshot? (if you go through the successive frames you will see the peak meter showing a maximum of 0db and a minimum of -18db with intermediate values of -2,5dB, -5dB, -10 dB, -15dB)

My understanding is that the peak meter should show the maximum level of the audio in the displayed frame. With this signal it should always be 0dB, whatever the frame you pick. Am I wrong?

If the peak meter shows the audio level at the beginning of each frame then the displayed value in the screenshot does not match the waveform.

It shows the RMS power level of all samples obtained from that frame.

Many thanks, it is perfectly clear now!

Oh, I think I have been a little bit too fast with my answer. With my sin signal am modulated at approx 50Hz normally Shotcut sees the same signal in each frame, only the phase is changed due to the fact that the modulating frequency is not exactly 50Hz. Also, with a sinus tone with its max at 0dB, the peak meter should show -3dB for the RMS value. Am I wrong? The following screenshot shows the peak meter at +2dB…

The RMS value in this frame

is the same as the RMS value in this frame:

and the peak meter shows a huge difference…

This topic is interesting to me. I should learn more about this.

I take back what I said about RMS. I was going off of memory since I knew we were using the MLT normalize module (based on the normalize command line tool, which is heavily based on RMS). However, upon looking it up, now I recall I added a separate filter based on code from a meter written by Steven Harris, who wrote the LADSPA plugins we include in Shotcut for many of the audio filters.

I think it is based on DPM.

Here is the MLT code Shotcut uses, which is easy to read if not entirely clear why some things are done. Shotcut sets iec_scale to 0 and instead does 20 * log10(audioLevel) for dBFS conversion.

We already know what the reference standard for this digital peak meter is.
Before reading this (my fault), I spent the whole morning doing tests to try to find out what was the standard reference (or measurement) method with respect to the most common options that I have in my DAW and in my loudness meters.

I generated a sinusoidal 1kHz tone with Audacity to contrast the measurement with different standards. However, it did not match any of the VST analyzer plugins that I use.

With this new information, I observe that this IEC standard 268-18-1995 (1995), has already been overtaken by other standards such as ITU-BS.1770 (2015) or EBU R128 (2014)The loudness meters that I have used for the comparison are based on these last two standards, so they will hardly coincide.
This is neither good nor bad, they simply can not match.
This applies only to the peak meter, so we have the Shotcut loudness meter (LUFS) based on EBU R128.
The use of this tool can help to standardize our criteria at the time of editing the audio of our video.
I did not delve into the advantages of one or another measurement standard (the different algorithms, the different commercial needs, the different platforms and entities involved). For me, each regulation is focused on a situation and that is how it should be understood.

I made some measurements of the peak meter response with 0dB sinus inputs created with Audacity (0dB=level1 on the Audacity peak meter). I did not plot on the graph the frequencies which are not multiples of the frame frequency (PAL 25Hz) because for these frequencies, especially at low values, the meter response varies a lot according to the phase of the signal (see the last values in the table). As you can see there are significant amplitude variations, most of them probably due to the ringing of the high pass filter. Notice also the dip at 12kHz (submultiple of the sample frequency):

This already exceeds my limited knowledge about this (although these days I learned some things that I did not know).
Anyway for a more professional audio edition surely an external audio edition is a possible option.
For my modest and scant videos, the audio filters in SC work perfectly.