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I was looking into the Apple II disk server (See below for background information) and curious if there is a tool that can actually convert .DSK image to .MP3 file, as the underlying c2t only supports WAV and AIFF format.

Does anybody have some experience on such kind of tool?

Background

C2T is a very interesting hack allowing to load disk images via the cassette port and write them onto Apple floppies (140k Disk II) without any previous OS support on the II side. Quite handy to bootstrap a naked hardware setup. Please see this article for more details about inenr workings and handling.

The 'Online Apple II Disk Server' is a connected project offering a simple web interface to offer download of many disk images as audio or in WAV/AIFF format. Never been so simple to bootstrap an Apple II find using modern toolsets.

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    Specifically liked the FAQ for c2t on the github site: "Yeah, but why?" - "You clearly do not understand the awesomeness of the Apple II, move along." Apparently, the author has a sense of humour. – tofro Jun 23 '19 at 9:03
  • What's your goal? If you want the audio files to be smaller for long-term storage, the best compression tool is c2t itself (i.e. just keep the images in .DSK format and "decompress" to playable audio with c2t as needed). – fadden Jun 23 '19 at 15:04
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    Why can't you convert it to a WAV then convert the WAV to MP3? – user253751 Jun 23 '19 at 21:54
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c2t converts from 140K disk images to audio files, though only AIFF or WAV files. It might take some experimentation to get MP3 encoding settings that work using the Apple II's LOAD command, though. c2t-96h encodes the 9600 baud audio data at 48kHz, so lame -V2 has a fair chance of working

c2t is used by the amazing Apple II Disk Server. It allows you to create Apple II disks on a II+ or IIe (but not a IIgs) by loading via the cassette port. It's basically magic.

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    The original Apple Game Server (by Blurry) which inspired this was even more magical. It booted the game over a serial port, found the disk RWTS on the fly and and replaced it with a serial port RWTS. That means it could handle full disk games that accessed the disk later - but over the serial port. This online version is simpler and more practical if you want to create disks. – Nick Westgate Jun 23 '19 at 10:26
  • @NickWestgate - yes, serial booting is exceptionally clever, but the ability to create system disks with your phone and an audio cable is pretty unbelievable until you see it done. – scruss Jun 23 '19 at 11:45
  • Just to clarify: c2t is a little like an archiver? You load the audio file into an Apple II with a Disk II and it writes a new copy of the disk, which you can then use? – Tommy Jun 23 '19 at 14:46
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    yes, that's exactly how c2t's disk image mode works – scruss Jun 23 '19 at 19:07
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    @Tommy It's basically a self-extracting archive. – Ross Ridge Jun 23 '19 at 20:35
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You may try to convert the offered WAV/AIFF files into an MP3 using some offline tool (preferred) like FFMPEG or an online conversion site like this one (no endorsement whatsoever).

It's a trial and error process, as conversion might change the resulting sound. This is especially true for conversion into MP3, as it's not only a lossy format (*1), but the process may as well include resampling. MP3's lossy compression is based on a psycho-acoustic model, which means it saves data by eliminating frequencies (or limits their amount) when assumed they are not noticed. Just, target of this 'sound' isn't a human ear, but a computer, dropping (or dimming) frequencies may render the whole transfer impossible.

FFMPEG does offer much control, but can't eliminate the basic issue, so enjoy the parameter-fiddling - or rather use a WAV/AIFF player instead. Most devices can handle them anyway.

*1 - WAV and AIFF are not, which as well may be the reason MP3 hasn't been offered in the first place.

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Is there any tool to convert .DSK to mp3 file?

That's a straight No, it can't be done that simple.

.DSK files are disk images, containing (usually) several files (of various type), while cassette data are single files (usually BASIC, but may be as well data, just with complete different handling than on a disk).

So the only solution here may be using some emulator to load files you want to convert (given they can be loaded single at all) and then save them as cassette output to MP3 (or wave). Or 'play' it via a sound port, connected to the IIe. If either is supported by the emulator that is.

But unless they are very simple self contained programs they won't be any useful after loading via cassette port, as they may want to use DOS function to access data - and there is no DOS on a cassette only IIe.

Ofc, there may be more to this, as the question is missing any description of the whole setup - and more important why you want to go that way.

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    It would be an interesting hack tho. Crack open the dsk and let the user pick a file, then read the file data and modulate appropriately to wave or MP3. Lots of fun code there... – Geo... Jun 22 '19 at 23:08
  • Maybe best not to answer if you don't know the target machine and its users … – scruss Jun 22 '19 at 23:22
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    @scruss Raffzahn is one of the most knowledgable members here on the Apple II; cf. retrocomputing.stackexchange.com/search?q=user:6659+[apple-ii] – Tommy Jun 23 '19 at 1:47
  • You may have overlooked the "an MP3 for the Apple II disk server" part, which takes care of the "conversion". – dirkt Jun 23 '19 at 4:46
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    @scruss Wooha! Guess what, that exeptional nifty hack of c2t and the 'Disk Server' completely passed below my radar - so I answered that question at face value with the little knowledge I have about the II. Mine just works (mostly) flawless since ~40 years, using a SSC for downloads. I guess the question wants some clarification, so non initiate ones will as well get the idea. – Raffzahn Jun 23 '19 at 5:24

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