Determining 5.1 audio by looking at waveform

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ls_milkyway
Posts: 2
Joined: Thu Sep 20, 2018 2:43 pm
Operating System: Windows 7

Determining 5.1 audio by looking at waveform

Post by ls_milkyway » Thu Sep 20, 2018 3:37 pm

Version Audacity: 2.2.2 portable
Version Windows: 7 ultimate 64 bit

Hi;
I just want to know how to determine genuine 5.1 audio?

For eg.

1) I have a DTS 5.1 AUDIO check tool from https://thedigitaltheater.com/index.php/tools/ and its waveform looks pretty nice (plz check image dts-tool)

2) I have a video file from internet which claims 5.1 channel audio (plz check image downloaded) with waveform clearly showing missing audio in channel 4 & 6.

I have 3 questions:

1) Is the audio not a 5.1 channel type, in the downloaded video?
2) How to determine the quality? for eg. using spectragraph etc.
3) If I convert/export audio from a source file in AAC to WAV, do channels mismatch (using aimersoft, audacity etc.) how to determine this situation?

Plz not: I don't have 5.1 system to immediately listen and check & I am currently using Audacity for only this purpose.

Any help will be highly appreciated.
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DVDdoug
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Joined: Fri Sep 10, 2010 11:30 pm
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Re: Determining 5.1 audio by looking at waveform

Post by DVDdoug » Fri Sep 21, 2018 10:10 pm

1) Is the audio not a 5.1 channel type, in the downloaded video?
I CAN believe what I'm seeing. It's up to the producers. Usually the of a movie dialog is in the (front) center, but it's a creative process. And, it wouldn't be unusual to have the rear channels silent for most of the movie, with occasional sounds coming from behind.

Also, a musical performance isn't supposed to have anything in the "point one" LFE. The LFE channel is supposed to be for low frequency effects (booms & explosions). All of the normal-musical bass is supposed to be in the other 5 channels. Then on a typical home theater setup with "small" surround speakers, the receiver has "bass management" that mixes all of the normal bass in with the LFE, and sends it all to the subwoofer.

Also if you play-back on a 2-channel stereo system, the LFE is supposed to left-out of the mix-down.

2) How to determine the quality? for eg. using spectragraph etc.
Your ears are better than a spectrogram or any other tool. Sometimes the spectrogram can show why it "sounds bad" but it's a poor way to judge quality. For example, lossy compression (Dolby AC3 or DTS) is designed to sound good without regard to what the spectrogram looks like. Background noise can be very annoying without "looking bad" on a spectrogram and I'm pretty sure I could make a terrible sounding file that looks good!
3) If I convert/export audio from a source file in AAC to WAV, do channels mismatch (using aimersoft, audacity etc.) how to determine this situation?
Everything should stay correct, but it's always a good idea to check (once you have a surround playback system). If you're making your own production it's pretty easy to make a test-file, with yourself saying "left-front", "center", etc., but if you are transcoding an existing file you'd have to some careful listening. Or... Maybe you don't have to listen that carefully if the main dialog comes-out the subwoofer or from the rear speakers! :D

ls_milkyway
Posts: 2
Joined: Thu Sep 20, 2018 2:43 pm
Operating System: Windows 7

Re: Determining 5.1 audio by looking at waveform

Post by ls_milkyway » Mon Sep 24, 2018 6:27 am

Thanks DVDdoug for quick and detailed answers.

I conclude that most of the software like Audacity, Mediainfo ..etc. can only tell what is the type of audio file or clearly state the wrong type of conversion/export.

One can only be 100% sure about quality by listening only.

Gr8 forum...

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