Hertz Overload by RETREAM [web]
HERTZ OVERLOAD MANUAL -------------------------------------------------------------------------------- END-USER AGREEMENT DEFINITIONS - In this agreement: "Software" refers to any and all files included in the Hertz Overload distribution archive. RIGHTS AND RESTRICTIONS - You can: make copies of the Software; distribute integral copies of the Software. You cannot: distribute modified copies of the Software; distribute separate parts of the Software; use (any part of) the Software for a profit without written permission. DISCLAIMER - THE SOFTWARE IS PROVIDED "AS-IS", WITHOUT ANY WARRANTY. TO THE FULLEST EXTENT ALLOWED BY LAW, THE AUTHOR CANNOT BE HELD LIABLE FOR ANY DAMAGE ARISING OUT OF THE (INABILITY OF MAKING) USE OF IT. USE AT YOUR OWN RISK. GOVERNING LAW AND JURISDICTION - This agreement shall be governed by the laws of the country of residence of the author at the time of the dispute. The author reserves the right to appoint the venue for the dispute. EPILEPSY WARNING - Some people are susceptible to epileptic seizures when exposed to certain flashing lights or light patterns, and they may even be unaware of it. The Software may cause problems to such people. Who experiences blurred vision, dizziness, disorientation, loss of consciousness, twitches, involuntary movements, convulsions while playing/watching the Software must stop doing so immediately and receive the due medical assistance. -------------------------------------------------------------------------------- GETTING STARTED Hertz Overload requires: * Amiga computer * AGA chipset * ~1.8 MB of RAM * ~56 MB of storage space * PAL-capable display * stereo loudspeakers To install Hertz Overload, unpack the LhA archive to any directory of your choice. To start Hertz Overload, run its executable from either shell or Workbench. To quit Hertz Overload before it ends, press the right mouse button anytime. During the loading of files or the streaming of music, you might need to keep the button pressed for a short while. If the device Hertz Overload is installed on is not fast enough to stream the music, audio stuttering or, in the worst case, a complete freeze might happen. Allocating many buffers with AddBuffers might have adverse effects. A stock Amiga 1200 with AmigaOS 3.1, able to trasfer blocks from a CompactFlash card at a rate of about 1 MB/s, can run Hertz Overload from it just fine (even after booting without startup-sequence, with as little as 10 buffers assigned to the partition Hertz Overload is installed on, and without running any additional software). Note for emulators: due to the high and odd audio frequency, emulators will have a hard time reproducing the audio exactly; the settings to use depend on what each specific emulator offers and on how it operates; as a general guideline, the output rate should be set to a high value starting from at least 141876 Hz; also, emulators should emulate the Paula chip timings exactly. -------------------------------------------------------------------------------- OVERVIEW Hertz Overload is a demo that focuses on delivering very high quality music on AGA Amigas, including base machines equipped with just a mass storage device (which is needed to stream the huge amount of audio data). "Very high quality translates" to: 2 true stereo channels, 14 bit resolution and 70937.9 Hz sample rate. While the first two parameters are common, the third one is not: it is reknown that the Paula chip can play samples at up to about 28 or 56 kHz in normal or doublescan screenmodes, respectively, and that, to reach higher frequencies, instead of fetching the samples from CHIP RAM through its DMA channels, it must receive them from the CPU - which is an extremely expensive method, as it requires the CPU to feed Paula with samples regularly and frequently, and thus has been rarely (or maybe never?) used. Hertz Overload employs exactly the CPU-based playback method, pushing things further as it also streams the samples from disk and, at the same time, displays and scrolls graphics - and manages to do so also on machines without accelerator boards. -------------------------------------------------------------------------------- TECHNICAL DETAILS The visual side of Hertz Overload is very lightweight and is handled by stock machines without effort. In fact, it is programmed with AMOS Professional and RETREAM's own ALS library. The initial music and the sound effects are normal tracker modules, played by means of the AMOS Professional P61 Extension (this was made necessary by the fact that AMOS Professional's Track Play command does not support or execute correctly the EDx command; maybe this could be worked around by reworking the music module using a speed of 1 tick, but it would be basically a useless exercise). The streaming music part (graphics scrolling included) is executed entirely by highly optimized assembly code (which disables AMOS Professional altogether so that it does not get in the way). The 14 bit playback method adopted is the classic one that plays the 8 most significant bits of a sample on a channel, at the maximum volume of 64, and the 6 least significant bits on the other channel on the same side, at the minimum volume of 1. Due to how Paula works, such method, to be precise, would require users to perform manually a tedious calibration process on their machines - that is definitely not something that watching a demo should require, so Hertz Overload is happy to make do with the uncalibrated output (which sounds good enough). Moreover, the high playback frequency should introduce another distorsion factor that affects those 6 least significant bits, at least according to the currently incomplete knowledge of Paula's inner workings. In theory, as a consequence of the counter-based volume management of the volume, any volume other than 64 should no longer work when the period (time between two consecutive samples) is less than 64 ticks - and Hertz Overload uses 50! However, tests performed on an Amiga 1200 rev. 1B showed that Paula handles the volume graciously (albeit not perfectly) also when the period is (much) smaller than 64 - and, in particular, that a volume of 1 is handled (almost?) perfectly also in conjunction with a period of 50 (which is what matters to Hertz Overload). -------------------------------------------------------------------------------- BACKSTORY The music track "Prockressions" was written while fiddling with the RETREAM guitar (shown in the demo itself) after it got fixed and overhauled. It was not made for Hertz Overload, but rather Hertz Overload was made for it. Thinking of a way to let others enjoy the music brought the idea of making an Amiga production, which immediately suggested the creation of a player capable of a sufficiently high quality. In the past, I had never tried CPU-based audio playback, but a quick experiment showed that it was doable and quite easy. That led to the development of a set of tools that generate and play sound files in custom formats aimed at minimizing the CPU load (later released separately as part of the AQA package). The tools proved that the Amiga can reach remarkably high frequencies (much beyond 70937.9 Hz), which pushed me in another direction: making something more artistic than a player, and that simply meant... a demo! Hertz Overload was being made for no specific demoparty. When it was almost finished (May 21st, 2024), I checked out which demoparties were about to come and found out that the 68k Inside 2024 was only a few days away! It looked like I could meet the deadline (May 25th) easily, but, of course, on the last day all that could go wrong went wrong, so I could not make all the little changes and additions that I had planned. -------------------------------------------------------------------------------- CREDITS Created by Simone Bevilacqua AMOS Professional P61 Extension by Chris Hodges The Player 6.1A by Jarno Paananen Testing by John Scolieri -------------------------------------------------------------------------------- rev. 20250130 www.retream.com/Hertz_Overload contact@retream.com (c) 2024 RETREAM
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