[PATCH 4/4] dsound: support 5.1 sound

[Chris Robinson]

On 01/06/2015 11:27 AM, Mark Harmstone wrote:
> +        case DSSPEAKER_5POINT1_BACK:
> +            device->speaker_angles[0] = M_PI/180.0f * -135.0f;
> +            device->speaker_angles[1] = M_PI/180.0f *  -45.0f;
> +            device->speaker_angles[2] = M_PI/180.0f *    0.0f;
> +            device->speaker_angles[3] = M_PI/180.0f *   45.0f;
> +            device->speaker_angles[4] = M_PI/180.0f *  135.0f;
> +            device->speaker_angles[5] = 9999.0f;
> +            device->speaker_num[0] = 4; /* Rear left */
> +            device->speaker_num[1] = 0; /* Front left */
> +            device->speaker_num[2] = 2; /* Front centre */
> +            device->speaker_num[3] = 1; /* Front right */
> +            device->speaker_num[4] = 5; /* Rear right */
> +            device->speaker_num[5] = 3; /* LFE */
> +            device->num_speakers = 6;
> +            device->lfe_channel = 3;
> +        break;

This doesn't look right. According to 
<http://www.dolby.com/us/en/guide/surround-sound-speaker-setup/5-1-setup.html>, 
5.1 should have the front-right/right speakers between +/-30 degrees max 
and +/-22 degrees min, and the back (surround) speakers between +/-110 
degrees max, +/-90 degrees min.

> +        case DSSPEAKER_5POINT1_SURROUND:
> +            device->speaker_angles[0] = M_PI/180.0f *  -90.0f;
> +            device->speaker_angles[1] = M_PI/180.0f *  -30.0f;
> +            device->speaker_angles[2] = M_PI/180.0f *    0.0f;
> +            device->speaker_angles[3] = M_PI/180.0f *   30.0f;
> +            device->speaker_angles[4] = M_PI/180.0f *   90.0f;
> +            device->speaker_angles[5] = 9999.0f;
> +            device->speaker_num[0] = 4; /* Rear left */
> +            device->speaker_num[1] = 0; /* Front left */
> +            device->speaker_num[2] = 2; /* Front centre */
> +            device->speaker_num[3] = 1; /* Front right */
> +            device->speaker_num[4] = 5; /* Rear right */
> +            device->speaker_num[5] = 3; /* LFE */
> +            device->num_speakers = 6;
> +            device->lfe_channel = 3;
> +        break;

This looks like it's based on OpenAL Soft (which is fine), which 
originally had 5.1side using 90 degrees. However I'm not sure it's 
really necessary for the two modes to use different angles. The current 
Git version of OpenAL Soft was changed so both 5.1 modes use 110 degree 
angles for the rear/side speakers, and the only difference is which 
output speakers they're mapped to.

It's not exactly wrong to put 5POINT1_BACK at 110 degrees and 
5POINT1_SURROUND at 90 (they're both within spec), but I think the 
intended difference is only for physical speaker mapping rather than 
positioning.