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Short:Determine Paula's max. replay rate
Author:post at (Rainer "No.3" Müller)
Uploader:post rraaiinneerr de (Rainer "No.3" Müller)
Requires:Asl.library V38 (=> Workbench 2.1)
Architecture:m68k-amigaos >= 2.0.4
Download: - View contents

New V1.0:

the hardware volume of the test tone can be set


1) Background
2) Setting up the replay rate
3) What is the minimum period?
4) How do I use MaxReplayTest?!
5) Hardware Volume
6) MaxReplayTest is "Feedbackware"
7) History
8) Disclaimer

1) Background

In the good old OCS times Paula and Audio was quite simple as there were
only NTSC and PAL Amigas. On both systems the maximum replay rate for
audio was something around 28.6 kHz.(*) With the upcoming of ECS and AGA
the maximum replay rate also increased and Amiga magazines and other
sources talked about a doubled maximum rate when using the new screen
modes i.e. something around 57.2 kHz.

But what is the real maximum replay rate using a specific screen mode?
I could not figure it out for over 20 years!  :-(  But now, everything
is different!  :-D

(*) there seems to be a second difference i.e. audio playback using the
audio.device vs. "direct DMA". As I only use the audio.device and do not
really understand the direct DMA playback, I am only talking about Paula
in combination with the audio.device.

2) Setting up the replay rate

If you play sounds using the audio.device you have to create an AudioIO
Request. In this structure you enter information about the memory
location of the audio data to be played, the volume and some more, but
there is no entry for a replay rate, only mysterious "period" !? This
period is calculated using the colorclock and the replay rate i.e.

   period = colorclock / replay rate

whereas colorclock is 3579545 Hz for NTSC systems (the hardware, not the
screen mode!) and 3546895 Hz for PAL systems. (*)

Altogether this means: the lower the period, the higher is the resulting
replay rate. In order to get to know the maximum replay rate you need to
know the minimum period. Regarding to the Autodocs the minimum period
is 124. Obviously this part of the Autodocs was never updated when ECS
and AGA were introduced.

(*) for sure you recognized the resulting limitations!? i.e. if you want
to replay with 22050 Hz (= 1/2 CD), on a PAL system the period is 160.8
which has to be rounded to 161 or 160. So the real resulting replay rate
is 22030 Hz or 22168 Hz but not 22050 Hz!! => the lower the period gets,
the bigger are the steps from a replay rate to the next one. For 44100 Hz
(= CD) this means you have to choose between 44336 Hz or 43788 Hz!

3) What is the minimum period?

By a few simple tests I could figure out, that the DBLNTSC, DBLPAL and
Productivity as well as Euro72 were capable to replay at least 44100 Hz.
On the other side Super72 does not manage the 44100 Hz.
=> there is a connection between the screen mode and the max. replay rate
=> to replay with ~44100 Hz a period of 80 is required, therefore the
   124 mentioned in the Autodocs is for sure no more true

To learn more about Graphics and Chip-Ram and how they affect Paula
I opened the thread "Grafik, Chip-Ram und Paula" in the forum.
There I got lots of feedback and explanations as well as the correct
key-words to search for.

=> the final answer I found in the EAB forum in a posting from Toni
Wilen (the WinUAE developer!) in the "15 bit 44 khz audio idea." thread:

  min period = (color clocks in horizontal line + 13) / 2 + channel

Unfortunately Toni's formula does not match the findings on my A1200.
So I adapted his formula a little bit:

  min period = (color clocks in horizontal line + 13 +1) / 2 + channel +1

this fomula can be written a bit differently:

  min period = (color clocks in horizontal line + 16) / 2 + channel

That's the same formula the user "ross" compiled in the "Minimum safe
Paula periods for PAL Amigas" thread also in the EAB forum:

  min period = (HTOTAL + 16) / 2 + channel

      +1: HTOTAL to totalCCK per line
      +8: Paula to Agnus DMAL delay
      +6: floppy DMA setup bits
      +1: align for successive shift
      /2: samples per word

And yes, you're reading correctly: every of the four Paula audio channels
has a different min period and therefore a different max. replay rate!
So to say, channel 0 is "the best" and channel 3 "the worst".

Now my goal was to write a program which is able to determine the
Paula's maximum replay rate and compare the "heard" results with above
formula in dependence of the used screen mode!

=> MaxReplayTest is the result!  :-)

4) How do I use MaxReplayTest?!

!! Warning !!

!! Turn down the volume before starting MaxReplayTest !!

After starting up a sine sound is played and depending on the volume
setting of your amplifier / speakers this sound may be very loud !!

So don't blame me if your speakers or your ears blow up, you have been
warned !!

1) Run MaxReplayTest from Shell or Workbench and select a screen mode
   (and change the number of colors if you want i.e. to increase the
   load on the Chip-Ram). The GUI opens and a sine sound is played on
   channel 3 (the "worst" one)  at  maximum replay rate.

a) Assumed that the adapted formula is "correct" channel 3 should play
   at its maximum replay rate. Now decrease the period one by one and
   therefore increase the replay rate to the next step.

   If you start to hear glitches or other parasitic noise effects, then
   the period is too low i.e. the replay rate is too high!

   => Congratulations, you found the maximum replay rate of the tested
      channel!  :-)

   Caution: it may take some to several seconds until you can hear a
            glitch, in other cases the glitches can repeat very quickly.
            Therefore don't decrease the period too quickly!

   Note: if you further decrease the period, sooner or later the
         glitches may disappear and the sine sound starts to sound too
         low-pitched as the replay rate no more increases!

   Go on with the next channel i.e. channel 2, press "set max" in order
   to set the replay rate to the maximum calculated level and start to
   decrease the period.
   Afterwards repeat the procedure with channel 1 and 0.

b) In the case you hear glitches right from startup or you can't provoke
   glitches by decreasing the period, try the other way round, increase
   the period. For whatever reason, perhaps the replay is already too
   high?!?  :-o

2) MaxReplayTest scanmodes

   shows some relevant technical data and the maximum replay rate of the
   installed screen modes e.g.:

Monitor       total color clocks   min. period   max. sampling rate

SUPERPLUS     232        ->        127 cc   ->   27928 Hz
A2024         226        ->        124 cc   ->   28603 Hz
EURO36        226        ->        124 cc   ->   28603 Hz
Film24        226        ->        124 cc   ->   28603 Hz
NTSC          226        ->        124 cc   ->   28603 Hz
PAL           226        ->        124 cc   ->   28603 Hz
HD720         196        ->        109 cc   ->   32540 Hz
XTREME        192        ->        107 cc   ->   33148 Hz
HighGFX       160        ->         91 cc   ->   38976 Hz
SUPER72       153        ->         87 cc   ->   40768 Hz
DBLNTSC       129        ->         75 cc   ->   47291 Hz
DBLPAL        129        ->         75 cc   ->   47291 Hz
EURO72        121        ->         71 cc   ->   49956 Hz
Productivity  121        ->         71 cc   ->   49956 Hz

5) Hardware Volume

The 65 different hardware volumes levels of Paula (64=maximum, 0=silence)
are achieved using PWM (pulse width modulation). At maximum volume no PWM
occurs, otherwise the PWM counters run at a frequency of 55.9 kHz (NTSC)
or 55.4 kHz (PAL). (To be exactly: it's the colorclock divided by 64).
This topic is discussed in the "Low-level workings of Paula" thread in
the EAB forum.

6) MaxReplayTest is "Feedbackware"

Yes, not Shareware, not Freeware, not Crippleware, but Feedbackware!  :-)

This means, if you use MaxReplayTest, then please give feedback on which
Amiga with which chips(et) you tested which screen mode (and the number
of colors) and what the resulting maximum replay rates for the four
channels were!  :-)

But why this?

Well, there are more differences between the different Amigas than only

The OCS A1000 & A2000A are quite 'similar' but the A500 and A2000B & C
are different to the first two. In addition, there are A500 and A2000
with a 1 MB Chip-Mem Agnus and some of them are even equipped with a
2 MB Chip-Mem Agnus and may even have an ECS Denise!

On the ECS side, the A3000 is a real 32 Bit Amiga i.e. everything
including the Chip-Mem is 32 Bit wide. The A500+ and A600 are also ECS
but they are still only 16 Bit Amigas i.e. the Chip-Ram is only 16 Bit
wide. In addition, in opposite to the A500+ the A600 is manufactured
in SMD technology.

=> it would be interesting to figure out if these differences have an
effect on the maximum replay rate. That's why I ask for feedback!  :-)

7) History

V1.0  02.07.2023  the hardware volume of the test tone can be set

V0.9b 03.07.2021  fixed a bug in the OpenScreen() return code handling

V0.9a 22.11.2020  fixed an issue in the PAL / NTSC detection

V0.9  09.11.2019  change frequency of test tone, toggle hardware audio
                  filter off and on

V0.8  30.12.2018  added the "set max" button, first Aminet version

V0.7  13.11.2018  "final" version

V0.6  02.04.2018  cleaned up the GUI

V0.5  20.03.2018  added the "scanmodes" option

V0.4  19.03.2018  the number of colors for the screen can be selected

V0.3  28.02.2018  now also works on Kickstart 2.0 with Workbench 2.1

V0.2  27.02.2018  first functional version, OS 3.0 or higher required

V0.1  27.02.2018  first version with a different approach which did not
                  work as intended

8) Disclaimer

I tested MaxReplayTest for hours and it caused no problems on and to my
system. Afterall you use MaxReplayTest on your own risk!

MaxReplayTest is pushing the (audio) hardware to its limits!

MaxReplayTest is for testing purposes only.

=> therefore MaxReplayTest is for people who know what they do and know
how much stress they can expect from their hardware without causing
damage to their hardware.

Contents of driver/audio/MaxReplayTest.lha
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[unknown]                 5903   19420  30.4% -lh5- 7b07 Jul  2 15:09 MaxReplayTest
[unknown]                  341     903  37.8% -lh5- 5e9c Dec 31  1982
[unknown]                 4367   10572  41.3% -lh5- 8924 Jul  2 16:21 MaxReplayTest.readme
[unknown]                  229     464  49.4% -lh5- cc4c Dec 31  1982
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 Total         4 files   10840   31359  34.6%            Jul  3 04:10

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