Re: [AD] Sound API

[Chris <kcat@xxxxxxxxxx>]

Ben Davis wrote:
> That would be a pretty scary curve. All normal audio would be in a tight 
> little 'band' (to misuse a term) with an evil DC offset, until it clips and 
> then it would jump all the way up to the top :)
>
> For 16-bit mixing, it'll be
>   0,0,0,...,0,0,0,16,32,48,...,65504,65520,65535,65535,...,65535
> i.e. steps of 16, but covering the full range. The precision is quite bad 
> actually. (This is with the old mixer of course.) But it does cover the full 
> range of output volume.

Right, a closer look at the original source more or less confirmed 
something like this. Still, each voice itself gets clamped to 14-bit (or 
15-bit if you use set_volume_per_voice(0)), which leaves very few voices 
before the mixer buffer wraps. And it still should be considered 14-bit, 
since 8-bit audio covers the full audio range but only has 256 levels, 
and Allegro's original only contains 16384 levels with the rest being 
set to max and mix.

> > And even with set_volume_per_voice(1), which would give you the default
> > volume level (half per channel if centered, or full if panned hard to
> > one side),
>
> Default? Default for what?

Default volume level. Where both channels added together would be full 
volume.

> So I guess there are two issues at hand: whether the output is the same when 
> set_volume_per_voice() is called, and whether it's the same when 
> set_volume_per_voice() ISN'T called.
>
>
> When set_volume_per_voice() isn't called:
>
> Is the default level the same? I don't think it would be wise to up it, since 
> games are relying on it. Back when I implemented set_volume_per_voice(), I 
> almost did change the default behaviour, but people didn't like it.

Well, the problem I see is when you implemented set_volume_per_voice, 
you couldn't change the default, or else you still risked overflow and 
wrap-distortion (you only had protection for 4 voices; anymore risked 
wrapping the buffer). My changes however, gives 255-voice overflow 
protection, and since Allegro only provides 64 maximum output voices 
there's no logical way that limit can be reached (whereas when 
set_volume_per_voice was put in it was still very easy to reach the clip 
table's limit) in existing programs.

- Kitty Cat