Re: [AD] Sound API

[Chris <kcat@xxxxxxxxxx>]

Ben Davis wrote:
> On Monday 17 May 2004 01:08, Chris wrote:
>
> > Allegro will never play at full volume without my patch. Remember, the
> > clipping table will clip it to a max of 14-bit output (lest output
> > wraps), and also the internal volume ranges were only 13 or 14-bit too.
>
> No, that's the _precision_. As I understand it, the old code used 14-bit 
> precision but scaled the output by 4, so the volume was the same as with the 
> new code. Are you sure there's an audible difference?

The volume is precision yes. And looking at the original code again, 
what I'm seeing is that 3/8ths of the 14-bit mixing range is clipped 
from both ends:
   /* clip extremes of the sample range */
   for (i=0; i<clip_size*3/8; i++) {
      mix_clip_table[i] = 0;
      mix_clip_table[clip_size-1-i] = clip_max;
   }
clip_size is 1<<14 in 16-bit output, and 1<<10 in 8-bit output. Anything 
within the two extreme ranges are topped, or bottomed, out, so you'll 
get audio ranging from 32 to 512, then clipped to 0 and 65535 if it's 
not within that range (in 16-bit output). If my math is right.

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), it is maxed out at 14-bit before mixing into the buffer, 
whereas my mixer maxes it out at 24-bit (then later scaled down as needed).

- Kitty Cat