Re: NetBSD/amiga audio questions: sampling rates, screenmodes, and the low-pass filter/LED state

[mlelstv%serpens.de@localhost (Michael van Elst)]

cme%ihug.co.nz@localhost ("Chris Edwards") writes:

>    u_int per=eclockfreq*5/freq;

>    if (per<124)
>        per=124;    /* must have at least 124 ticks between samples */

>Wouldn't this only be necessary when the system is using a plain old PAL/NTSC 
>screenmode?

No.


>So, is there anything potentially "bad" about loosening the restriction on the 
>period in this way (or even removing it altogether)?

The period also determines how soon playback of a buffer completes and
thus determines the interrupt rate for reloading the buffer pointers.
Therefore you should have at least some limit, otherwise you could
send the machine into a tight interrupt loop by chosing a too high
playback frequency.



>My second question is about the low-pass audio filter (and the corresponding 
>power LED brightness) on many Amiga models.  It seems that NetBSD just leaves 
>the filter in whatever state it's in when it's booted, which is on (LED 
>bright) on my 1200.  It would be nice for there to be a kernel option to set 
>the initial filter state to "off", since playing audio in 14-bit at 44.1 kHz 
>with the filter on is a bit pointless!

Maybe the audio driver should just chose the filter setting depending
on the sample frequency ? Anything below 8kHz should have the filter
enabled to reduce aliasing distortion.


-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."