Computer Audio Tape Formats

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Tue Dec 17 18:13:00 2002

>From: "Dwight K. Elvey" <dwightk.elvey_at_amd.com>
>
>>From: tlindner_at_ix.netcom.com
>>
>>> Here's one:
>>>
>>> http://www.kim-1.com/usrman.htm#E
>>
>>Ahh, this is really diffferent!
>>
>>This uses:
>>
>>'0 bit' - 18 square cycles at 3700 Hz.
>> 6 square cycles at 2400 Hz.
>>
>>'1 bit" - 9 square cycles at 3700 Hz.
>> 12 square cycles at 2400 Hz.
>>
>>Both are the same length (7.452 microseconds).
>>
>>As you can probably tell, I am currently anaylizing this at a very low
>>level.
>>
>>--
>>tim lindner tlindner_at_ix.netcom.com
>>
>
>Hi
> Here is one that is even a little different still.
>It is what is called Manchester encoding, using biphase
>clocking. You don't indicate 1 or 0, you indicate a change
>by a quick clock and no change by a long clock.
> It looks something like this:
>
> ___ _ ___ _
> |___| |_| |_| |______

Opps! Shuld have been:
 ___ _ ___ _ ___
    |___| |_| |_| |___|


>
> Depending on past history, this might be:
>
> 0 0 1 1 0 0 0
>
> or
>
> 1 1 0 0 1 1 1
>
>
> This is the type of encoding used on my Poly88 for
>what they call PolyPhase. This runs at 2400 baud.
> There is a standard called Byte format that uses 300 baud
>and the two tones 1200 and 2400.
> Besides the type of encoding, you also need to know
>what the record formats looks like. Do you have one long
>record for the entire file? What does the header look like?
>Is it synchronous or asynchronous? Is there parity, check sum,
>CRC or ECC?
> There are a lot of things that need to be built up into
>a complete tape decoder. A tape writer would be used
>by more than a tape reader. One should only need to read
>the tape once but many people would often like to create
>a tape from that same data. You really want both.
> One should also note that most audio tape to digital
>inputs on these old computers filtered the signal some
>to optimize the audio signal for decode. This was done
>on both read and write of the signal.
>Dwight
>
>
>
Received on Tue Dec 17 2002 - 18:13:00 GMT