Re: [hatari-devel] Improved YM2149 sound

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 05/05/2012 22:13, David Savinkoff wrote:
> Hi,
>
> This patch is for more accurate YM2149 sound. Sounds better also.
> Tested ok, specifically on: Decade demo (quartet screen), Madness demo,
> Blubber demo, sh11inv demo.
>
> Hunk 1) Fixes a typo of mine.
>
> Hunk 2) Improved YM2149 math model.
> Hunk 3) "
> Hunk 4) "
> Hunk 5) "
>
> Hunk 6) Discard frequencies higher than 80% of nyquist rate.
> Hunk 7) "
>
> Hunk 8) DC level correction for high frequencies 'quartet mode'
> Hunk 9) "
>
> David

>   	Tone3Voices&= ( Env3Voices | Vol3Voices );
>
>   	/* D/A conversion of the 3 volumes into a sample using a precomputed conversion table */
> +
> +	if (stepA == 0&&   (Tone3Voices&  YM_MASK_A)>  1)
> +		Tone3Voices -= 1;    /* DC level correction for high frequency 'quartet mode' */
> +
> +	if (stepB == 0&&   (Tone3Voices&  YM_MASK_B)>  1<<5)
> +		Tone3Voices -= 1<<5;
> +
> +	if (stepC == 0&&   (Tone3Voices&  YM_MASK_C)>  1<<10)
> +		Tone3Voices -= 1<<10;
> +
>   	sample = ymout5[ Tone3Voices ];			/* 16 bits signed value */

Hello

regarding hunk 8, this means that when StepA == 0, then a volume of 0x14 
for example will become 0x13. What is the math reason leading to 
decrement the voice volume by '1' for quartet mode ?


Nicolas