We analyzed the sound pressure of the YouTube video in Japan .
On YouTube, loudness normalization is introduced. Loudness normalization on YouTube lowers the volume of the video whose sound pressure is too high, but does not raise the volume of the movie whose sound pressure is too low.
If you have lots of videos with too little sound pressure on YouTube, you can increase the volume played on YouTube by raising the sound pressure to the extent that sound quality is not impaired.
Question
How much movie is too small sound pressure on YouTube?
As mentioned above.
Does the sound pressure drop if the YouTube video length is long?
As the length increases, the probability that the peak of the waveform will increase by chance will increase. If you use a limiter, you can suppress those peaks, but if you do not use a limiter, the sound pressure may decrease as the length increases.
From this, if you examine the relationship between length and loudness, it seems to be a material to judge whether the limiter is used or not. There are other factors related to length and loudness, so we can not make a judgment alone, but once we examine the relationship between length and sound pressure.
※ Because almost all of the movies have failed analysis
※ The video list is described in Appendix
Analysis measures
Loudness
It is an indicator of the sound pressure. Calculated with ITU-R BS.1770-3.
Loudness Range
It is an indicator of dynamic range. We calculated and calculated the window length and overlap length of EBU TECH 3342. Window length 0.4 s, overlap length 0.3 s.
Analysis Result
Loudness
Loudness histogram
Loudness cumulative density distribution
Loudness time series
Loudness Range
Loudness range histogram
Loudness range cumulative density distribution
Loudness range time series
Relationship between loudness and loudness range
Loudness vs Loudness range scatter plot
Loudness vs. Loudness average and standard deviation
Length
Length Histogram
Length cumulative density distribution
Length time series
Relationship between length and loudness
Length vs Loudness Scatter plot
Length vs Loudness average and standard deviation
Discussion
How much movie is too small sound pressure on YouTube?
Looking at "Loudness cumulative density distribution", except for "Lantis", the loudness of 90% or more of the video is -14 dB or less.
Since the loudness calculation formula used this time is different from that of YouTube, I can not show the line that loudness normalization is applied any more, but if I refer here , I think that -14 dB is sufficiently small, so sound pressure other than Lantis If you raise it, there seems to be a possibility that the volume at the time of playing on YouTube will rise.
Does the sound pressure drop if the YouTube video length is long?
According to "Loudness vs Length Average and Standard Deviation", such a fact is unlikely.
" Haruan " may be YouTuber which is fully compliant with loudness normalization .
Loudness normalization fully compliant What is YouTuber?
YouTuber understands YouTube 's loudness normalization specification and uses it well .
What is Loudness Normalization?
YouTube automatically adjusts the volume between videos.
Have you seen "detailed statistics" from the right click menu of YouTube videos?
Please pay attention to "Content loudness" in this. This value is a reference when YouTube performs loudness normalization.
If "Content loudness" is positive, YouTube will lower the volume. If it is minus, the volume remains unchanged.
Two facts about sound
To make good use of loudness normalization, the following two facts are important.
A. There is a trade-off relationship between sound pressure and sound quality
B. Larger volume sounds better
How to make good use of loudness normalization
On YouTube, since loudness normalization works, there are points where the sound volume does not rise even if the sound pressure is raised . It is the point where the above "Content loudness" becomes 0.
Since the sound pressure and sound quality are in a trade-off relationship, increasing the sound pressure so that the "Content loudness" becomes 0 or more on YouTube, the volume does not rise, so the larger the volume, the better the sound is heard Instead, only the sound quality goes down .
So, the best solution when raising a video on YouTube is to set "Content loudness" near 0 or below 0 .
"Harukanaru" video content loudness "
Please take a look at "Content loudness" of recent Hara video. I think that every video is near 0 dB .
Video of 2018/12/02 ("Content loudness" 0.0 dB)
Video of September 23, 2018 ("Content loudness" 0.0 dB)
In other words, Haruan's movie is the best balance of sound pressure and sound quality on YouTube. It is unusual for it to happen unintentionally, so it may be intentionally done.
However, in the video before a while, "Content loudness" deviates from 0 dB .
2018/05/25 movie ("Content loudness" -1.7 dB)
Video of 2017/11/12 ("Content loudness" - 8.5 dB)
Recently, it may correspond to the loudness normalization.
Summary
It was an article that YouTuber " Haruan " might be fully compliant with the loudness normalization .
For YouTuber applications and news applications, YouTube's loudness normalization criteria are sufficiently low, so it may be natural to respond like SEO from now on .
In order to raise the highest sound quality video to YouTube, you need to know the YouTube loudness normalization specification.
However, YouTube's loudness normalization specification is not published. Some people have already been investigated, but specific calculation formulas are not known.
I tried to estimate the formula for loudness normalization on YouTube.
YouTube loudness normalization specification
The following is a summary of the survey results.
The loudness normalization is performed in a manner that the loudness of the sound source is adjusted to the loudness target value as much as possible within a range where the peak does not clip.
The loudness of the sound source is calculated with its own specifications, but by replacing the weighting curve of Short-term loudness of EBU TECH 3341 with the following and taking the maximum value of Short-term loudness, it is possible to obtain the accuracy of 1 dB Can be approximated.
Research policy
We will investigate the framework of YouTube's loudness normalization in detail and the details of loudness calculation.
A large frame of YouTube's loudness normalization
I think that probably it looks like the following when referring to here .
The loudness normalization on YouTube is done in a way that the loudness of the sound source is adjusted to the loudness target value as much as possible within the range where the peak does not clip. When written with an expression, it becomes the following.
Compensation (dB) = Min (- Peak, Target - Loudness)
Peak is the peak of the sound source, Loudness is the loudness of the sound source, Target is a constant, the loudness target value, and Compensation is the correction gain. The overall volume changes uniformly by the amount of Compensation.
Right click on a YouTube video and the content loudness seen from the detailed statistical information is equivalent to Loudness - Target.
Loudness calculation formula on YouTube
YouTube's loudness calculation formula seems to be using its own one. So, I need to guess.
Consider the following model with reference to ITU-R BS.1770-3.
Equalizer -> Cut by window -> Convert to LUFS -> Gating -> Aggregation
Equalizer
Weight each frequency by an equalizer.
In previous experiments, K-weighting adopted in ITU-R BS.1770-3 and other popular weighting did not apply, so estimate direct frequency characteristics.
Cut by window
Cut out the waveform with the Rect window.
Window length and overlap ratio are parameters.
For reference, the momentary and integrated parameters of ITU-R BS.1770-3 and EBU TECH 3341 have a window length of 400 ms and an overlap length of 100 ms (the overlap ratio is 75%). The short-term loudness parameter of EBU TECH 3341 has a window length of 3 seconds and an overlap length of 2.9 seconds or more (overlap ratio is 96.7% or more).
Convert to LUFS
Calculate the RMS of the extracted waveform and convert it to LUFS with Log 10 (RMS).
It also corrects to be 0 with stereo 1000 Hz sine wave. The correction amount for ITU-R BS.1770-3 is -0.691 dB.
Gating
In order to eliminate the influence of silence time on loudness, we discard small sounds among multiple RMS values obtained by cutting out.
Refer to ITU-R BS.1770-3 and EBU TECH 3342 and perform Absolute threshold gating and Relative threshold gating.
The parameters are the respective Threshold values. I also try patterns that do not do gating.
For reference, the parameters of ITU-R BS.1770-3 and EBU TECH 3341 are Absolute Threshold -70 LKFS and Relative Threshold -10 dB. Parameters for calculating the Loudness Range of EBU TECH 3342 are Absolute Threshold -70 LKFS and Relative Threshold -20 dB.
Aggregation
Take the average or maximum of multiple RMS values remaining in Gating.
ITU-R BS.1770-3 takes an average, but it seems there is a possibility of using the maximum value of Short-term according to this .
Test video used for parameter estimation
Prepare a test movie to estimate the parameters of the loudness calculation model.
According to here , it seems that there is a possibility that loudness normalization will not be applied if there is not a certain number of playback numbers, or it will not be applied unless some time has elapsed since posting. Without preparing test videos on their own, there are enough playback numbers, select some of the existing videos that have been posted enough times, and make them test videos.
A list of test videos is described in the Appendix.
Equalizer parameter estimation
By using a sinusoidal test movie with a constant volume, you can eliminate effects other than equalization on loudness. Using this we first estimate the frequency response of the equalizer.
For the sine wave sound source of various frequencies, measure the content loudness on YouTube and estimate the frequency characteristics by taking the difference from the RMS of the sound source. The estimation result is below. For detailed data please see Appendix.
The result was unstable, for example, the results were different depending on the animation even at the same frequency above 16 kHz, so in the following discussion, we will only use data below 15 kHz. Extrapolate with linear interpolation for 44 Hz or less and 15 kHz or more.
Parameter estimation other than equalizer
Next, fix the frequency characteristics of the equalizer and estimate parameters other than the equalizer.
Calculate the loudness of various videos with various parameters. Compare with the loudness (Content Loudess) calculated by YouTube and look for the parameter with the least error. The test video list is described in the Appendix.
Parameter combination with the least error was window size 3 seconds, overlap rate 96.7%, Max aggregation, standard error of error was 0.9 dB, maximum error was 1.7 dB. It is the maximum value of Short-term loudness of EBU TECH 3341. The loudness target value is -10.3 LUFS.
With this, you can estimate the loudness calculation method of YouTube.
Here's how to edit videos on iPhone. This time I will do it with free iMovie.
Install iPhone video editing application iMovie
Install iMovie from the App Store.
Create a project
When you start it, it becomes the screen on the left, so press the plus sign on the project tab. Then select a movie.
Load movie
Select the material video. Multiple selections are possible.
Cut video
When you tap a movie, an editing menu like the left picture appears. After choosing scissors and choosing Split, you can cut the video at the point you select like the right image.
Sort videos
Touch and hold the movie to change the order of the movies by drag & drop.
Adjust the volume of movies
You can adjust the volume by tapping the video with a choice and selecting the speaker in the Edit menu.
Export movie
By pressing the completion button at the upper left of the screen and pressing the send button at the bottom of the screen, you can export the movie to various applications. For this time, save to the photo library, so choose Save Video. When you select export settings, the export will start.
Increase the quality of audio (publicity)
Using our AI Mastering, you can increase the quality of the edited movie. Please try it with a video made with iMovie!
The efficiency of video editing and the quality of the resulting video will vary greatly depending on which application you use. Therefore, selecting an application is important.
I will introduce a video editing application other than iMovie at a later date.
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