Some Revision music tracks don't loop seamlessly

[Yarn366]

Some of the music files distributed with Revision, even those that loop, have extra silence at the beginning and/or end of the file, producing a small gap whenever they loop. Three tracks where this is quite noticeable are both ambient themes of Hell's Kitchen and Gunther's battle theme; these aren't the only ones with the problem, though.

This behavior is what I would expect from MP3s and anything converted from MP3, as the MP3 format doesn't preserve exact length without nonstandard extensions.

[hugelogan]

Ouch! The Hell's Kitchen one is my fault. Thank you for pointing these out

[Yarn366]

I could list every file that has this problem, but I think it suffices to say "a lot of them." However, if you really want me to make the list, I'll do it.

Are you guys sure the music didn't go through an MP3 (or other lossy) intermediate?

[hugelogan]

Yeah a list would be helpful. I don't involve mp3 anywhere in the workflow, everything goes straight from lossless to .ogg. I'm sure it's the same for John

[Yarn366]

OK, below is the list of tracks that should be looked at. If a listed track has a separate intro track, then that should be looked at as well.

01_NYC_Combat
01_UNATCOHQ_Ambient
01_UNATCOHQ_Combat
01_UNATCOHQ_Convo
02_Bar_Ambient
02_NYC_Combat
02_Street_Ambient
03_747_Convo
03_Airfield_Convo
03_AirfieldHeliBase_Ambient (plus extra click about 9,900 samples into loop track)
03_BrooklynBridgeStation_Ambient
04_Gunther_Combat
05_UNATCOMJ12lab_Ambient
06_Canal_Ambient
06_Canal_Convo
06_HeliBase_Ambient
06_HongKong_Convo
06_HongKong_ConvoSpecial
06_Market_Ambient
06_MJ12lab_Ambient
06_MJ12Lab_Convo
06_Versalife_Ambient
06_Versalife_Combat
06_Versalife_Convo
08_NYC_Convo (not due to extra silence)
08_Street_Ambient
09_Graveyard_Ambient
09_Graveyard_Convo
10_Chateau_Ambient
10_Metro_Ambient_Alternate
10_Paris_Convo
11_Cathedral_Convo
11_Everett_Convo
12_Cmd_Ambient
12_Gas_Ambient
12_Tunnels_Ambient
12_Vandenberg_Combat
15_Area51_Combat
15_Bunker_Ambient

[Jerion]

Hi!

I'll take a look at these this week. Can you elaborate on your process for determining when a track has extra silence?

At no stage in the workflow was the MP3 format involved; on my end, these are compressed directly to 192 Kbps OGG from the AIFF or WAV formats.

Occasionally looping issues are actually caused by CPU performance being taxed during playback (or a standalone player having a delay before restarting a loop), rather than a problem with the file itself, and we need to make sure that the issue doesn't even partially lie there.

[Yarn366]

I checked the music files by loading them into Audacity, splicing together the tracks in the order of intro-loop-loop or loop-loop (depending on whether there's an intro track), and visually examining the areas around the splice points.

The main things I looked for were a sudden cut to silence at the end of a file audio and a sudden cut from silence at the beginning of a file. If any of those existed, I added the file to the list. If they didn't, I looked for visible seams at the splice points. If those were present and the track had an intro, I added the file to the list (because if there's an intro track, there's no reason for seams to exist). If seams were present and the track had no intro, I listened to the area around the splice point; if I heard a click or something similar, I added the file to the list.

So, no, I wasn't simply listening for seams, so CPU load and loop delay are highly unlikely to be culprits.

[Jerion]

The plot thickens. In at least one case (probably more), the silence is not actually silence, but extremely quiet noise. Relatively easy to eliminate in editing, but I would love to know what created it in the first place, and why it appears on some tracks but not others.

[Yarn366]

If Audacity was involved in the workflow, then that might be the cause. By default, when reducing the sample size, Audacity applies a small amount of noise for the purpose of dithering. More information on this can be found on this page: http://wiki.audacityteam.org/wiki/Dither (the dither algorithms are explained near the bottom)

Other audio programs may have similar behavior. Just play with the dither settings (if they exist) and see whether that affects added noise.

[Jerion]

Originally posted by Yarn366:

If Audacity was involved in the workflow, then that might be the cause. By default, when reducing the sample size, Audacity applies a small amount of noise for the purpose of dithering. More information on this can be found on this page: http://wiki.audacityteam.org/wiki/Dither (the dither algorithms are explained near the bottom)

Other audio programs may have similar behavior. Just play with the dither settings (if they exist) and see whether that affects added noise.

Audacity isn't involved in the workflow on my end, but the idea there might be close to the mark. Interesting.

[hanfling]

Dithering while quatization isn't a bad thing. You will get get noise in any case, but by dithering you can get the noise in the shape (as in frequency distribution) you prefer.

https://www.xiph.org/video/vid2.shtml has a nice explaination about that.