Surround Sound in Music
I have been doing some exploration in to quadraphonic audio.
Quadraphonic is a system that never got formalized as a standard. The closest standard that you find is 5.1 or 7.1 sounds system that you find in home theater systems. You can fit a quadraphonic sound, 4 channels, into a 5.1 system, however the left and right speakers for front and back, in a 5.1 systems often are not placed in a perfect square.
The back speakers are called surround speakers, because they are just slightly at the back of the listener. They are also for added ambiance in movies, they are not necessarily a full sound source.
Still Stereo, 5.1 and 7.1 are source based system. You render the sound for the location of your speakers.
This is changing with Dolby Atmos which is an object based sound system: what are the objects in your virtual 3D that emit sounds, they then get rendered on any speaker configuration.
Let's get back to quadraphonics.
I rendered a quadraphonic track into various formats and uploaded to YouTube:
- a 360 video with ambisonic sound
- a normal video with 4 channels
- a normal video downmixed to stereo (2 channels)
- a normal video downmixed to binaural audio (2 channels)
- a normal video with 5.1 channels with center and LFE silent
I use a utility called youtube-dl to see what YouTube did of the files.
- the audio of the 360 video is rendered, mainly on headphones, based on what the listener is watching. It is not great for TVs, YouTube in fact does not render the 360 view on TV players.
- the 4 channels is downmixed to 2 stereo channels
- the stereo or binaural stay in their format
- the 5.1 channels exist in downmixed stereo and in 5.1. Therefore the player could play either of the audio files.
If you look at the files created by YouTube for the 5.1 upload you see that the larger sizes are in 5.1.
$ youtube-dl --list-formats https://www.youtube.com/watch?v=rPODqX7JW5M [info] Available formats for rPODqX7JW5M: format code extension resolution note 249 webm audio only DASH audio 66k , opus @ 50k, 2.16MiB 250 webm audio only DASH audio 88k , opus @ 70k, 2.85MiB 140 m4a audio only DASH audio 130k , m4a_dash container, mp4a.40.2@128k, 4.59MiB 251 webm audio only DASH audio 173k , opus @160k, 5.61MiB 256 m4a audio only DASH audio 196k , m4a_dash container, mp4a.40.5, 6.92MiB 258 m4a audio only DASH audio 389k , m4a_dash container, mp4a.40.2, 13.75MiB 160 mp4 256x144 144p 95k , avc1.4d400c, 30fps, video only, 2.03MiB 278 webm 256x144 144p 103k , webm container, vp9, 30fps, video only, 2.83MiB 242 webm 426x240 240p 237k , vp9, 30fps, video only, 4.28MiB 133 mp4 426x240 240p 292k , avc1.4d4015, 30fps, video only, 5.40MiB 243 webm 640x360 360p 448k , vp9, 30fps, video only, 9.15MiB 134 mp4 640x360 360p 663k , avc1.4d401e, 30fps, video only, 11.69MiB 244 webm 854x480 480p 883k , vp9, 30fps, video only, 15.74MiB 135 mp4 854x480 480p 1285k , avc1.4d401f, 30fps, video only, 23.93MiB 247 webm 1280x720 720p 1882k , vp9, 30fps, video only, 28.91MiB 136 mp4 1280x720 720p 2520k , avc1.4d401f, 30fps, video only, 50.56MiB 248 webm 1920x1080 1080p 2744k , vp9, 30fps, video only, 46.64MiB 137 mp4 1920x1080 1080p 4908k , avc1.640028, 30fps, video only, 77.85MiB 271 webm 2560x1440 1440p 7900k , vp9, 30fps, video only, 160.67MiB 313 webm 3840x2160 2160p 14994k , vp9, 30fps, video only, 259.44MiB 18 mp4 640x360 medium 507k , avc1.42001E, mp4a.40.2@ 96k (44100Hz), 18.00MiB (best)
I select to download format code 258, which is the biggest audio file in mp4 format and I check using ffmpeg its audio format and especially how many channels it has.
$ youtube-dl -f 258 "https://www.youtube.com/watch?v=rPODqX7JW5M" [download] Destination: _-rPODqX7JW5M.m4a [download] 100% of 13.75MiB in 00:03 $ ffprobe _-rPODqX7JW5M.m4a Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '_-rPODqX7JW5M.m4a': Metadata: major_brand : dash minor_version : 0 compatible_brands: iso6mp41 creation_time : 2019-10-14T08:21:16.000000Z Duration: 00:04:57.45, start: 0.000000, bitrate: 387 kb/s Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 12 kb/s (default) Metadata: creation_time : 2019-10-14T08:21:16.000000Z handler_name : ISO Media file produced by Google Inc.
As you can see the Stream #0:0 is 48kHz with 5.1 channels.
To help you test your sound system, I uploaded an original 5.1 movie on my site and using the HTML5 video tag, your browser should play the movie with all its channels.
This video uses HTML5 <vi
<video width="100%" preload="" controls=""> <source src="files/Surround-5.1.mp4" type="video/mp4; codecs="avc1.4D401F,mp4a.40.5"> <span class="error">Error: Source Statement Failure - Format not supported in this browser?</span> </video>
I also uploaded this movie on YouTube:
However I tried to play it on my web browser, the youtube app on xfinity, or the youtube app on PS3 and all I got was the downmix stereo, despite the fact that a 5.1 format does exist on YouTube and that browsers are capable of rendering a movie with 5.1 audio.
Searching the Internet it appears that the PS4 may have a 5.1 YouTube player. Many people are commenting that YouTube TV does not play 5.1 movies like Netflix does, therefore they don't see the benefit of YouTube Movie premium.
So, will we see support for 5.1 on YouTube soon? time will tell.
You may have seen 5.1 videos on YouTube, and got the feeling that your sound system renders them in 5.1. Not exactly, these videos have only 2 channels, but there are a few ways to encode 4 or more channels into 2 channels using matrix encoding with optional phase shift(Wikipedia).
This is what Dolby Pro Logic II, also know as DPL II, does using matrix technology. On Amplifiers that do not understand DPL II the sound is just stereo with a relatively good quality downmix. You should be able to upload a DPL II video to YouTube and have the proper amplifier decode it into 5.1. DPLII seems widely supported as it seems it comes part of any movie sound system that has the Dolby logo. However, if you upload a 5.1 video, YouTube will not encode the audio in this format but just downmix it to stereo.
Waveforms of the 5.1 test file (L, R, C, LFE, LS, RS):
Converted to DPLII:
DPL II format is not without its challenges, after all there is lot of signal compression and mixing going on to fit 5.1 channels into 2 channels.
For other distributions systems, like Bandcamp, they only support stereo audio. What people have done, is offer a physical medium SACD or DVD to purchase or download a specific file from something like dropbox to get the quadraphonic or 5.1 file.
It seems that Sony is working with Deezer, Tidal and a few others to offer HiFi 360 Sound on selected Sony headphones. Will that take?
Additionally, companies are offering surround headphones, with many drivers per head. It seems the gaming industry has a marktet for players that want to hear what's happening in their back...
However if you want to listen to a quadraphonic or surround track in its perfect form, you still have to rely on physical media.