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The VHS video "Up and Running with the D70" published by Roland in 1990 is a handful source for becoming familiar with the synths user interface.
You can find it here on Youtube

More on the Roland D70

Polyphony - Yes it looks good. 30 voices. But you will only get that much voices if the patches you use have only 1 tone assigned. The fat and interesting patches will easily use the maximum of 4 tones. So playing that big chord by playing 4 keys will take up 16 voices. And then you'll have voice-stealing when you play another 4 key-chord after that. You'll wish you could poly-chain those D70 synths to solve this. Hum, well, you could buy a second D-70 and play them both with the same patch and that will solve your polyphony problems. Still it is possible to do sequencing with this synth as long as the patches have not many tones. And 1 tone patches can sound quite good when sequencing.

Interface not always helpful - You can only select a different performance/patch/tone by using the bank/number buttons. Regretfully the arrow buttons, dec and inc, and the value wheel won’t work here.
Write button is also text input button - with the D-70 design quite symmetric and well looking, it is not that handy that this button (and the enter button) has 2 functions. When programming, most of the time you have finished the tone and then you want to give it a name. After that I do mostly press save(write). But you can't write a performance/patch/tone after typing the name, because the write button also works as text input button. You'll have to move away from the name input field to make it possible to write…And that is when programming a new bank, is really a lot. I think it was better if Roland did choose for the caps button also a sort of shift function, so the numeric fields could also give you the special signs, making place so the write and enter button would not have been used for text input. Or just simply assign 3 input/presses for some of the numeric keys.

Display Beep - The maddening display beep, is also a famous D70 legacy, like the Red glue.

Good output - This synth has CD quality sound, and has really low noise output.

Flexible - Yes, the D-70 is some kind of sample player with added filter. A kind of U-20 updated but not in all ways: polyphony is not more that the module even though you can play a lot of tones at once for a patch. And that is a limitation you can hear. There are some synth parameters but it is somehow limited. Still you can make a lot of variations of sounds. Thanks to the somehow difficult system of tones, patches and performances and internal effect processor.
Each tone can have it's own velocity setting in a patch. You can can make a patch with some tones with velocity, others without. You can make switch from one tone to another with velocity, or you can make a mix with velocity (soft tone playing only one voice, louder playing the other voice mixes in).
You can in one patch mix reverb sounds, chorus sounds and output another sound dry.

LFO slows down - when playing more keys, the speed of the LFO slows down. This is ok for some leslie organ type of sound, but most of the time it is an effect you don't want. As there is no fix by firmware (as far as I know), it seems to be a synth hardware problem. It is a strange thing this happened as the synth is like an updated U-20. More processing power is however likely needed by the filter section (x4 tones). And because of the limitations of allowed CPU to be used this processing power is too low. Roland did make changes to get things better: Changed CPU (Main Board) from one wait to no wait, to improve processor speed in system 1.11. Even a change in CPU (B step CPU) with system 1.12. But the LFO is till unstable.
I tested this and the LFO is much steadier when bypassing the filter. Even with one tone on, adding the filter to a tone slows down the LFO.
With bypassed filter, up to 3 tones with LFO on will be reasonable steady. But with 4 tones for a patch with LFO on and filter bypass for these tones there is an audible slow down also. So the processing power of the D-70 seams to be too weak for good handling of the LFO. (tested on system 1.14).
Also LFO Syncing of tones is quite hard when playing about 4 tones (even with only 1 tone on).
The D-70 is not the only ‘U series’ product that has this problem. The earlier U-110 module also has the LFO slowdown problem.
ADSR slows down - I did not notice this earlier, but the ADSR is also affected in speed when there are many tones on and a lot is also asked in terms of polyphony.

C1 position reset? - I programmed the upper zone in the C1 settings to transpose an octave. In this way, it is easy to make an octave sound, because the lower part stays the same. Just put the C1 slider to the maximum position for an octave.
This works great, but when (probably) reaching the polyphony limit (easy to reach when having 4 tones on) the C1 setting will reset to zero and therefore you'll lose the octave sound. Seems a problem with the synth itself, I should probably replace the slider with a new one.

No compare/audition function

So you edited the sound, but is it that different than what you started with. There is no way to hear the original sound when you are editing. The only was is to save your edited work in a free memory space and then you are able to compare it with the original patch or tone.

New saved tone will not automatically change the path in the patch

This happens to me quite often. Making an patch, but need to edit one of the tones. You change the sound of the tone because it needs to be adjusted, but you save it to a new location (because the original tone is used in other patches, and that sound you don't want to change). So lets say I have tone A-22, changed and saved this in A-23. When going back to the patch editor it sounds good, but the tone sound you hear is still that of the edited A-22 with the right name you gave: still the path is not correct. You still need to change it to A-23 before saving, because the editing of A-22 is temporary. Tip here, always press after saving an patch the same patch and listen to it, you hear if all paths are ok, or that you have forgotten to change the tone link.

Editing the sound of a patch does not alter the sound of more of the same tones

Ok. This ruined some of my sound edits. Say you have a patch with Tone A-11 used in L-1, L-2 and U-3. So the same tone is used to create a patch. When editing the sound, for example the tone of L-1, changes only effect to this part of the patch. Even that the same tone is used, or you save the changed A-11 tone, the D-70 won't update the changes made to the tone which is also used in L-2 and U-3. Only after reloading the patch, L-2 and U-3 are updated.
This is probably because you can edit one part of the patch with live playing (say change filter), that will only effect what part you selected and it should. Also handy when wanting a variation of the sound, and save to a different location. But on the programming side this is tricky when saving the edited sound to the same location.
Key problems! After some years of use, the keybed had a matrix problem and the synth was sounding very strange with some combination of keys. Now 20 years further on I also have the famous Red Glue problem: Keyweigths dropped, the glue anywhere and about 50% of the keys not making any sound. This is what is looks like.
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In the Tone Edit menu, there are two pages where you can edit the DLM. Doing this on the Tone PRM is logical. Strange choice of the programmers for also adding this to the Tone Pitch page? Well, of coarse you always have to tune after changing the DLM settings.
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