Re: MD: data onto audio MD, for the depraved
>I am sorry Dave, but I don't think Sony currently sells a MD data deck. >It is my understanding that they used to sell them but they were very >slow and have been discontinued for years. So, if you want to store >digital computer data to a minidisc, you will most likely be using >modern equipment and have to contend with ATRAC. This puts you back to Before I got a day job (and a pay drop) I used to work in a wafer fabrication plant (making IC's) There were machines in there called nikon steppers which had MD Data drives there I think! It said MD DATA on the drive but it had no make on it. They were bought in 1993-94. Only catch was it was for the old magneto optical discs which were about the same size as a 1.4 floppy but about 10mm thick. They held 640 and 850 MB. The looked the same as MD's only bigger. When I first heard of MD's This is what I saw advertised. When I finally got an MD Portable MZR-30 I thought that Audio MD's and Data MD's might be different sizes and use the same technology. I remember B4 Ireland had any in the shops acutally drawing the dimensions of a MD disc out on paper and being wonderstruck by the tiny size. (also thinking that all Id ever need would be 5-6 discs) To This day, Ive never actually seen a MD data disc without its plastic wrapping. I just presume they look the same as an audio MD. Bryan http://bullets.gothic.ie - To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
Re: MD: data onto audio MD, for the depraved
=== = NB: Over 50% of this message is QUOTED, please = = be more selective when quoting text = === I am sorry Dave, but I don't think Sony currently sells a MD data deck. It is my understanding that they used to sell them but they were very slow and have been discontinued for years. So, if you want to store digital computer data to a minidisc, you will most likely be using modern equipment and have to contend with ATRAC. This puts you back to using Howard Chu's serial data encryption method or what you retrieve from the MD will not likely be the same as the data you saved on it. Dave Hooper wrote: > > I have just read all of that, and it was utterly pointless: > MD Data decks already exist and here is the very simple reason why: > > ATRAC DATA IS DIGITAL > > MiniDiscs simply store digital data > > You can use the MiniDiscs themselves to store any kind of digital data you > like > > You do NOT have to store the data using the ATRAC system !! > You do not need to 'encode' (and I use the term liberally and reluctantly) > data as an audio stream first !! > You simply need an MD-Data compatible deck (e.g Sony have a few) > > - Original Message - > From: "Howard Chu" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Sunday, December 17, 2000 10:06 AM > Subject: MD: data onto audio MD, for the depraved > > > > > OK, ATRAC is lossy and frequency-based. You cannot feed it linear data and > > expect it to come back exactly as it was before. It divides an input > sample > > into 512 spectral elements, which are themselves grouped into 52 > > nonuniformly distributed bands. Frequencies within the same band are > > considered maskable by the center frequency of that band. > > > > If you really really really want to record data through ATRAC: Pick a > > sequence of frequencies, and consider them "bytes" or "words." Pick them > far > > enough away from each other (in frequency) so that they cannot mask each > > other. > [...] > > - > To stop getting this list send a message containing just the word > "unsubscribe" to [EMAIL PROTECTED] -- Jim Coon Not just another pretty mandolin picker. mailto:[EMAIL PROTECTED] If Gibson made cars, would they sound so sweet? My first web page http://www.tir.com/~liteways - To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
Re: MD: data onto audio MD, for the depraved
I have just read all of that, and it was utterly pointless: MD Data decks already exist and here is the very simple reason why: ATRAC DATA IS DIGITAL MiniDiscs simply store digital data You can use the MiniDiscs themselves to store any kind of digital data you like You do NOT have to store the data using the ATRAC system !! You do not need to 'encode' (and I use the term liberally and reluctantly) data as an audio stream first !! You simply need an MD-Data compatible deck (e.g Sony have a few) - Original Message - From: "Howard Chu" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, December 17, 2000 10:06 AM Subject: MD: data onto audio MD, for the depraved > > OK, ATRAC is lossy and frequency-based. You cannot feed it linear data and > expect it to come back exactly as it was before. It divides an input sample > into 512 spectral elements, which are themselves grouped into 52 > nonuniformly distributed bands. Frequencies within the same band are > considered maskable by the center frequency of that band. > > If you really really really want to record data through ATRAC: Pick a > sequence of frequencies, and consider them "bytes" or "words." Pick them far > enough away from each other (in frequency) so that they cannot mask each > other. [...] - To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
MD: data onto audio MD, for the depraved
Much technobabble ahead. Read at your own peril. OK, ATRAC is lossy and frequency-based. You cannot feed it linear data and expect it to come back exactly as it was before. It divides an input sample into 512 spectral elements, which are themselves grouped into 52 nonuniformly distributed bands. Frequencies within the same band are considered maskable by the center frequency of that band. If you really really really want to record data through ATRAC: Pick a sequence of frequencies, and consider them "bytes" or "words." Pick them far enough away from each other (in frequency) so that they cannot mask each other. I.e., pick frequencies that all lie in separate bands. Also, each word must be some multiple of the ATRAC block size in length: 11.6ms (long block, 512 samples), or 2.9ms (short block, 128 samples). If you use one frequency from each band, you can encode 52 words per block. The ATRAC bit allocator only has enough bits to encode on average 3.4 bits per sample. The "bit size" of your words is translated to amplitude of the chosen frequencies. Assuming a short block, that means you have 3.4 bits/sample * 128 samples = 435.2 bits per block to work with. 435.2 / 52 words gives 8.37 bits per word. You can set the amplitude of each word within a ~8 bit dynamic range, let's say exactly 8 bits for convenience. So, to encode 52 bytes of data, select 52 frequencies and set their amplitude according to the byte value. Take these 52 sine waves and sum them together into a 2.9ms chunk. You need to select the amplitude range carefully, to prevent overflow. With 52 waves being added, you need 6 bits of headroom, so your sine waves' amplitude should range from 3-10 bits in value. Continue generating these 2.9ms chunks for each successive 52 byte block of input data. Of course, what you're doing here is *expanding* your input data by a factor of 5 so that it can feed thru ATRAC's 5:1 compression unmolested. You will be able to store 140MB of raw data in 75 minutes, not exactly a wonderful data transfer rate. Comparable to old streaming tape drives. I suppose if you only want to use MDs for archival backup, that's tolerable... Oh: decoding the data now requires you to essentially recreate ATRAC's own encoding step: you want to run an FFT or MDCT over the audio data to split it into frequency bands, and derive the energy of each frequency band of interest, which becomes your original data byte. The integrity of the transfer depends on the MD's ATRAC encoder using the same 2.9ms frame boundaries that you used. I'm not sure how to guarantee this, other than insuring that your computer's S/PDIF output is completely idle when you're not streaming data to it. You'll also probably need to generate a 2 second preamble, and use Synchro Record on the MD deck, to give it a chance to lock into the digital signal and start recording. You may need to include a dither signal to keep the digital signal valid during runs of zeroes and such. Best bet is to gzip your input data first, which will pretty much guarantee that you're feeding non-zero data into the system. So: if anyone still feels like using their audio MD deck for computer data storage, there you go. Have fun. (The ravings of someone who has spent 20 of the past 36 hours reading Sony patents...) -- Howard Chu Chief Architect, Symas Corp. Director, Highland Sun http://www.symas.com http://highlandsun.com/hyc - To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
