Descriptive Problem Summary:

- Setting `echo` to a list containing all the defaults echo values outlined in https://www.byond.com/docs/ref/#/sound/var/echo will down-mix stereo to mono.

- Setting `echo` to a list containing 18 null values will down-mix stereo to mono.

- Editing any value in a list of echo values will down-mix stereo to mono.

- Setting `echo` to an empty list down-mixes stereo to mono.

- Setting `echo` to `null` does NOT down-mix stereo to mono. Any other random value, like `1` or `"lol"` also does not down-mix.

- Setting `environment` to any preset (besides -1) down-mixes stereo to mono.

- Setting `environment` to `null` does NOT down-mix stereo to mono.

- Setting `echo` to any list will down-mix it, but if you set the same sound's `echo` BACK to `null` afterward playing it, and play it again, it will be stereo. The same applies to environment.

Numbered Steps to Reproduce Problem:

Test case: https://github.com/MrMelbert/byondsoundtest

- test_sound(modified echo, environment) -> mono
- test_sound(null , environment) -> mono
- test_sound(list() , null ) -> mono
- test_sound(null , environment) -> mono
- test_sound(null , -1 ) -> stereo
- test_sound(null , null ) -> stereo

Running the test case will play a distinctly stereo sound. It's some random "Stereo test" I found on youtube.

In some situations, the sound will be down-mixed to mono, i.e you hear it in both ears. In other situations, it will remain stereo, and thus only be audible in the left ear.

Expected Results:

Honestly, I'm not sure what is 'expected'.

My understanding is that when editing some of these values, you will need to down-mix out of necessity to apply reverb.

But when there is no change from default, I would not expect it to need to down-mix. This makes it impossible to - as an example - pre-fill in /sound's echo list for easy editing, without down-mixing ALL of your sounds.

However, I'm obviously not that knowledgeable about how the EAX2 sound system works - finding documentation on it is hard now-a-days. So I could be straight wrong about that.

But ultimately if this IS functioning as intended, it would be nice if the documentation for these vars mentioned that down-mixing will occur if you use them.

Did the problem NOT occur in any earlier versions? If so, what was the last version that worked?

I tested 513, and it performed similarly, outside `env = null` causing down-mixing. (Which was changed in 515 I believe)

Workarounds:

Avoid using echo or environment unless your sound is already mono