Welcome, Guest. Please login or register.

Author Topic: Maximum Paula sample rate in PAL mode?  (Read 9040 times)

Description:

0 Members and 1 Guest are viewing this topic.

Offline rvo_nl

  • Lifetime Member
  • Hero Member
  • *****
  • Join Date: Oct 2006
  • Posts: 860
    • Show only replies by rvo_nl
Re: Maximum Paula sample rate in PAL mode?
« Reply #14 from previous page: October 15, 2012, 06:20:49 PM »
Now that this thread has gone a bit quiet, can someone please explain the relation between screen refresh frequency and audio playback frequency? I cant imagine Im the only one being puzzled by this. I mean Ive always known about a certain connection, but not why it's there.
Amiga 1200 (1d4) Kickstart 3.1 (40.68), Elbox Power/Winner tower (450w psu), BlizzardPPC 603e+ @240mhz & 060 @50mhz, 256MB, Bvision, IDE-fix Express, IndivisionAGA, 120GB IDE, cd, dvd, Cocolino, Micronik Keycase, PCMCIA Ethernet, Ratte monitor switcher, Prelude1200, triple boot WB3.1 / OS3.9 / OS4.1, Win95 / MacOS8.1
 

Offline bloodline

  • Master Sock Abuser
  • Hero Member
  • *****
  • Join Date: Mar 2002
  • Posts: 12113
    • Show only replies by bloodline
    • http://www.troubled-mind.com
Re: Maximum Paula sample rate in PAL mode?
« Reply #15 on: October 15, 2012, 06:32:05 PM »
Quote from: rvo_nl;711570
Now that this thread has gone a bit quiet, can someone please explain the relation between screen refresh frequency and audio playback frequency? I cant imagine Im the only one being puzzled by this. I mean Ive always known about a certain connection, but not why it's there.
It's all related to how much data can be pumped across the custom chip bus. The more graphics data you push across the bus the less time is left for audio data... Well, that's a bit simplistic, but you get the idea :)

Offline Zac67

  • Hero Member
  • *****
  • Join Date: Nov 2004
  • Posts: 2890
    • Show only replies by Zac67
Re: Maximum Paula sample rate in PAL mode?
« Reply #16 on: October 15, 2012, 06:47:12 PM »
All Amiga chipset DMA is tightly coupled to horizontal video timing. Paula's audio data has one DMA timeslot per scanline allocated for each of the audio channels. The bus is 16 bit wide, so two samples can theoretically be played during each scanline. Some internas of the chipset limit the theoretical 31+ kHz max sample rate to 28867 Hz (according to AHRM).

So, if you increase the horizontal scan frequency Paula is allocated more DMA slot time (shorter intervals) and can increase the sample rate without underrunning DMA throughput.

Another way is to feed data through the CPU - but that would require very fast IRQ handling and produce significant overhead. It should also be possible to use the Copper to feed data into the D/A registers (like in CPU mode) but apparently nobody has done it yet.
 

Offline amiga-penn-wchester

  • Full Member
  • ***
  • Join Date: Dec 2011
  • Posts: 104
    • Show only replies by amiga-penn-wchester
Re: Maximum Paula sample rate in PAL mode?
« Reply #17 on: October 15, 2012, 07:15:36 PM »
yeah, previous post was pretty much the most correct.  It's the reason why DSS (Digital Sound Studio) changed screenmodes when you selected HQ sampling or playback.  Some other stereo sampling programs (VideoMaster AGA's audio sampler) wanted to be in a dbl mode to have HQ sampling.
 

Offline rvo_nl

  • Lifetime Member
  • Hero Member
  • *****
  • Join Date: Oct 2006
  • Posts: 860
    • Show only replies by rvo_nl
Re: Maximum Paula sample rate in PAL mode?
« Reply #18 on: October 15, 2012, 09:55:08 PM »
Understood. Thanks for your replies. I assume that is the reason why you can get higher frequency playback when you run Workbench in RTG mode.
Amiga 1200 (1d4) Kickstart 3.1 (40.68), Elbox Power/Winner tower (450w psu), BlizzardPPC 603e+ @240mhz & 060 @50mhz, 256MB, Bvision, IDE-fix Express, IndivisionAGA, 120GB IDE, cd, dvd, Cocolino, Micronik Keycase, PCMCIA Ethernet, Ratte monitor switcher, Prelude1200, triple boot WB3.1 / OS3.9 / OS4.1, Win95 / MacOS8.1