Drum store code question

F

Findlay

Member
I would like to apologise in advance if this is not the right place for this thread but you guys know the answer to most things so I thought I'd ask!

I'm still working with old tapes recorded on my Tascam 244 in '89. I have about half a dozen songs on which track 1 has been used to record the sync code from a Roland Tr626 drum machine. A few years back I managed to digitise these recordings after kind advice from jpmorris and other guys here. I managed to sync the Roland to playback from a DAW and recorded the individual drum voices and the sync seemed fine at the time but I find now on one song it has wandered off a little - not by much but enough to be annoying. So I thought I'd have another go using a the Tascam DP-32sd I just bought. I've had loads of help from the Tascam forum on this and after transferring the 244 tracks onto the new recorder I can sync up beautifully with the Roland and finally play the drums in perfect time. But I had an odd problem on the way which falls into both analogue and digital camps.

I had to restore the drum pattern onto the Roland from a "drum store" track I had made at the end of the cassette used on the 244. I used a JVC deck running at normal speed for this all those years ago. I didn't have the DP-32 or Roland in the same location as the old tape so I thought I could just digitise the drum store recording using another digital recorder and load this up onto the DP-32 later for restoring the drum pattern on the Roland. I used the same JVC deck I'd used 30 years ago (and working well) to play back the store code into a Tascam DP-01fx. But when loaded onto the DP-32 I was unable to restore the drum pattern onto the Roland - it just didn't want to know. I tried all sorts of levels but no go. I had to wait until I could bring the original cassette back home to where I have the Roland and record the tone directly on to it for it to be able to restore the drum pattern - incidentally using a different cassette deck for playback.

I'm at a loss work out what was going on here! I'd appreciate any thoughts......
 
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If you recorded the data as a straight WAV file (uncompressed PCM) it should Just Work. I've done that a lot with ZX Spectrum games, which were distributed on cassette because a disk drive cost four times as much as the computer did.
Straight WAV will work, however, if you MP3 compressed it, that could easily render the data unplayable. Computer data on tape is generally recorded as a stream of square waves, at two different frequencies, for zero and one. What the Spectrum does is it counts the pulses, using the time between each zero crossing to figure out if it's one frequency or the other.

However, MP3 and similar compression schemes work by decomposing the audio into sine waves, and stripping out the ones a human wouldn't be able to hear. Unfortunately a square wave requires a very large number of sine waves to reconstruct, so when the MP3 codec throws most of them away, you end up with something that no longer resembles a square wave. You get spikes and ringing and lots of spurious zero crossings which will confuse the FSK decoder in the Roland. (I wrote an FSK codec myself a few years ago as a random project).

If might be worth loading the unreadable audio data into Audacity and taking a look to see whether the squarewaves look reasonably clean. Not sure if there's a way to fix it, but if you posted a screenshot it might help diagnose the problem.
 
DrumStore.jpg

Thanks for the reply jp. I recorded the drum store tone on the Tascam DP-01 fx as WAV (16/44). I've posted a screenshot of a magnified part of the recording in Audacity. It looks doesn't look much like a square wave - maybe this is the problem?
 
Hmm, that looks good enough for it to work. I'm not seeing any spurious blips, though I do notice the higher frequency blocks are quieter. If I remember, I'll have a look at some of the Spectrum waveforms when I get home and post them here for comparison.
 
DrumStoreDP32.jpg

Thanks jp. I've just tried the experiment of recording the drum store code restored on Roland directly from the original tape on the DP-32. When I play this back into the Roland it verifies and works ok. I've posted this file which seems to differ a bit. It seems there is something about the tape intermediate which messes things up! I've had the same happen with 5 songs now so it would appear to be a real effect.
 
spectrum_fsk.png

Interesting, mine is even more ratty than yours. Yeah, you might need someone more familiar with the Roland to help here. Playing the recording out of the digital recorder should just work.
 
Thanks for your help again - I'll try to see if anyone else with the TR626 has experienced this.

I wonder if I'd recorded the tone on the 244 in the first place if it would have digitised ok? I'm not sure why I used another deck. The sync tone works fine. In the old days I installed a defeat for the dbx on channel 1 for the sync. I had to remove this a while back, otherwise I'd try it out.
 
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