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Old 12th October 2011, 07:14 AM   #1
neazoi is offline neazoi  Greece
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Default cassette tape erasure

Hello,
When you write one side of an ordinary stereo cassette does the erasing head erases both channels? i.e. can I record the left channel first and when finished then the right one?
If not, is there any way to do it?
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Old 12th October 2011, 07:23 AM   #2
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It erases both channels.
It would require significant rebuilding of the deck to do what you want.
- Unbolt the erase head and move it away from the tape (do not disconnect it, it's usually part of the bias oscillator circuit).
- Add a switch to disconnect the left track head when recording the right track.
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Old 12th October 2011, 07:56 AM   #3
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With Adobe Audition (and likely many others) you could put separate programs on the 2 channels and simply record both channels at once and make no changes to the cassette deck.

G
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Old 12th October 2011, 08:06 AM   #4
neazoi is offline neazoi  Greece
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Quote:
Originally Posted by stratus46 View Post
With Adobe Audition (and likely many others) you could put separate programs on the 2 channels and simply record both channels at once and make no changes to the cassette deck.

G
Yes, that was what I thought as a solution. The purpose is to write computer data (represented by audio tones) onto the cassette, for an old micro.

Using computer programs like the one you mentioned or wavepad, two channels could be separated and recorded at once on the tape. This is OK for pre-recorded stuff, e.g. games that only need to be read and will double the capacity of the tape.
A tape counter and a hand written index at the back of the tape will prove useful in that case.
But if you want to save other things on the tape from the computer later on, you cannot use tha same tape, as you will erase both channels at once. So you have to use another tape and record only one of the two channels for mono operation.
So If using a stereo head, I would use this only for pre-recorded data that does not need to be altered...
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Last edited by neazoi; 12th October 2011 at 08:10 AM.
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Old 12th October 2011, 08:11 AM   #5
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Are you multi-tracking, or just trying to get double record time? Either way, I agree it isn't very practical with an ordinary deck, and second the digital solution.
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Old 12th October 2011, 08:15 AM   #6
neazoi is offline neazoi  Greece
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Originally Posted by sofaspud View Post
Are you multi-tracking, or just trying to get double record time? Either way, I agree it isn't very practical with an ordinary deck, and second the digital solution.
This is just for doubling record time. Since data tapes do not need to be high fidelity, I could also reduce the tape speed to 1/2 or even less to achieve even more data written onto the tape I guess. I do not know the lowest speed limit though, I would have to try it by driving the motor with a lm317 variable regulator.
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Old 12th October 2011, 08:25 AM   #7
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I've never before thought about joining the two technologies... modem signals as a wav file for an old tape storage micro. There might be user groups that could have useful info.
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Old 12th October 2011, 08:27 AM   #8
neazoi is offline neazoi  Greece
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Originally Posted by sofaspud View Post
I've never before thought about joining the two technologies... modem signals as a wav file for an old tape storage micro. There might be user groups that could have useful info.
Oh, this was really used very much in these old micros. You may see the one I have made zx80 zx81 computer

Thank you all for your answers
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Old 12th October 2011, 09:25 AM   #9
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It's probably much easier to do this in software and record in one pass on a standard deck. But, in the interest of completeness, there is an option of multitrack cassette decks to check out. You never know, it might work for you.

Talk to some musicians around your home area.

The cassette-based 4-track portable studio machines (TEAC/Tascam, Fostex) operate in one direction recording 4 tracks. Because they're used for multitracking, each channel is recorded/erased/left alone individually, as required.

So, you could easily record on the track that represents the L channel only, and then go back and do the R channel only. Because they're multitrack, you can also play back Track 1 while recording Track 3 in sync (ie in real time, not with the delay that would be caused by the different location of record and playback heads in a standard non-multitrack deck).

You could probably find one used for a (very) reasonable price; they're not used by anyone much anymore since computer multitracking is just as portable, just as cheap, and far more versatile than these old systems are.

You will have to get your head around how these systems record tracks versus standard cassette. Looking at a ribbon of cassette tape, there are four tracks available. Normally tracks 1+3 are for the currently usable side, 2 + 4 for the other. If you were to be able to play 2 + 4 in a standard cassette deck, they would play back backwards.

Because the tape is flipped over for playback of the other side, what was 2 +4 now become 1 +3, so the stereo recording or playback doesn't require moving or selecting anything different.

A multitrack cassette deck operates on all 4 channels, and is meant to record/playback is only one direction (if you flip the tape the "wrong" way, all four tracks would play backwards). So, record on tracks 1 + 3, flip the tape over, and record on tracks 1 + 3 again (in essence, forcing your recording regimen to match the standard cassette deck's regimen). If you use tracks 2 + 4 they will be backwards when you attempt to play them back on a standard cassette deck.

I believe some operated at standard cassette 1 7/8, but most operate at double-speed for greater fidelity (3 3/4 ips). If the machine you find cannot switch between 1 7/8 and 3 3/4, then you can compensate by recording tones at half frequency ... ie if you want a 500 Hz tone on a cassette deck, but all you have is a multitrack machine that operates at 3 3/4 only, record a 1000 Hz tone instead. It will play back at half frequency at the half speed.

A bonus of this relationship is much better LF fidelity, as a 80 Hz tone is well recorded while on a standard cassette frequencies below about 50 Hz are difficult to encode. A drawback is HF frequencies will be limited since you will only be able to encode about 17K, which will play back at 8500 Hz.

If the HF response on a standard deck is important to you, consider hunting down the rarer 1 7/8 machines or a dual-speed machine. I don't believe TEAC ever made one, but perhaps someone else did ... I think Fostex might have ... they were cheaper than 144's.

You can transpose pitch for complex audio programming in software, if necessary, to get the correct pitch relationship of 1:2.

You could hunt eBay or classifieds for a deck. A "wanted" ad wouldn't hurt ... lots of these machines are sitting around in basements, unused. I've seen TEAC Portastudio 144's selling for $20 and $50 (MSRP 1980 $1200.00).

If you do get a 144, you have to be aware that these machines were purppse-built for maximum live recording quality and certain options you might expect to find on a cassette deck were simply deleted, partly to preserve cost but also partly to prevent anyone from straying away from a controlled quality specification. Recording live music on a cassette in any serious fashion is not trivial.

So, for example on the 144, Dolby B NR is always on. You may have to find a way to defeat that, since it will affect HF playback at standard speed. Bias is always CRO2 (also variously marked on decks as "High", or Type II, or 70 us) so no normal bias tapes will work properly.

Also with the 144, you must use only use TDK SA90 tapes; other tapes won't erase properly on overdubs (recording over a previously recorded passage). You might have to bulk erase and record only once (although this doesn't mean you can't record each track individually, just once).

The least expensive ones are the ones you actually want ... the fancier units will be the ones that are less compatible (NR including DBX encoding always on, standard-cassette incompatible track spacing, etc).

There were other units made by a host of the usual companies (Akai, Yamaha, Sansui, Marantz) but they are rare. Musicians actually bought the TEAC and Fostex decks; the others, not so much.

As for sound quality, they are not bad in the right hands. The Bruce Springsteen album "Nebraska" was recorded on a 144 and the cassette was used as the master tape for the album.
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Last edited by Johnny2Bad; 12th October 2011 at 09:53 AM.
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Old 12th October 2011, 09:53 AM   #10
neazoi is offline neazoi  Greece
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Thank you very much for the very informative post and the time taken to write it!
As I said, this is for computer data recording, which requires only tones of low frequency to be written. Even voice 300Hz-3KHz could be too wide for this purpose, so a high fidelity deck is not needed at all. Actually I am building it using a stereo microcassete drive to reduce physical size even more.
The amplifier used is this one http://www.microwave.gr/giannopk/zxc...sseteschem.jpg
I have made the playback section with great success, I have to build and test the record one to see how it goes as well. My drive has a passive erase head (magnet) so the lower left circuit is not needed. Between the R/W head and S1A another switch will be added to select one of the two head channels (assuming a stereo head as discussed previously).
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