short : Determine Paula's max. replay rate author : (Rainer "No.3" Müller) uploader : post rraaiinneerr de (Rainer "No.3" Müller) type : driver/audio version : V0.8 requires : Asl.library V38 (=> Workbench 2.1) architecture : m68k-amigaos >= 2.0.4 Filetype : application/x-lzh-compressed Size : 9.28K Date : 1-Jan-19 Download : 💾
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. 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! 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 :-D 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! :-) Don't talk so much! 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) @ maximum replay rate (*). (*) 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 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 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 OCS, ECS and AGA! 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! :-) History ------- 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 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.
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