question: does the MB have background tuning?

[F5D]

BobTheDog, you are right. I just tried this as well. You can enter the tuning mode either by pressing the two buttons exactly at the same time, or first holding panel and then pressing Kbd Track! In any case, I think it is good that we found this issue and now we have proper way to launch the auto tune mode. I am sure many MatrixBrute owners who face the synth being out of tune and think it is possibly faulty did not actually enter the auto tune mode nor saw the Tune text, but thought it was fine because the manual does not mention the text appearing. Arturia should add to the manual that you should see a scrolling "Tune" text on the display, when the auto tune does its thing. It takes about 2-3 seconds to complete, at least the text disappears then.

[F5D]

Related to tuning. There is slight variance in the result of the auto tune after running it multiple times, maybe +/- 2 cents between the two oscillators. If you program a typical lead sound with Osc 1 and 2 both having just a saw wave and levels almost equal, you get the typical phasing (or beating), because the two oscs cancel each other with slow beating. However, programming such a sound is sometimes difficult right after running the autotune, because to get such slow beating, you need to tune both oscs really close to each other. It seems that the detents in the fine pots make this slightly more difficult, because you easily get too far from the tune of the other oscillator. However, you can go past this issue by tuning both oscillators off the center, where the detent is not a problem. Then, you just use the master tune pot of the synth to set the correct tuning. However, this does not necessarily sound in tune with Osc 3, if you want to use it.

Another interesting thing I found is that especially after running the auto tune, and you are trying to find the very slow beating between the two oscillators, very often the synth stops the beating completely and kind of "sucks" like a magnet the frequency of the other oscillator to match perfectly the tune, like using sync even if it is not in use! You need to tune the oscillator again off and try to come back closer to the frequency of the other to get the slow beating. I find this behaviour peculiar. I am actually wondering, does the auto tune process end immediately after the text disappears, or does it continue on the background for a while, because there is often very strange random variation in the beating, especially after running the auto tune. The longer you have played since auto tuning, the easier it is to find the slow beating without the two oscillators getting to the exact same frequency like magnet.

Btw, I must mention that even though some of my posts may sound negative, I like the synth very much and am here just to solve these issues / understand the features for the best of all users, and some of the issues found so far are not even issues, but need to be better commented in the manual. This Brute is really special, has put smile on my face many times while discovering something new. It is definitely a character machine with all these little features.

[DrJustice]

...
Another interesting thing I found is that especially after running the auto tune, and you are trying to find the very slow beating between the two oscillators, very often the synth stops the beating completely and kind of "sucks" like a magnet the frequency of the other oscillator to match perfectly the tune, like using sync even if it is not in use!
...

Could be sympathetic synchronization (injection locking). Known to happen when several oscillators can minutely affect each other through adjacency and common circuitry.

[BobTheDog]

I think the snap of the tuning is not an oscillator type thing, it is caused by the fine tune knobs snapping back to the dead zone.

You can show this by mapping the mod wheel or macro knobs say +3 to OSC 1 pitch and -3 to OSC 2 pitch, now use the mod control to set the beating between oscillators.

First thing you will notice is that the resolution is much higher than the fine tune knobs so you can get much slower beatings going on, also there is no snap back in tuning like you get with the fine tune knob.

P.S. The mod knobs values are saved with the preset so I am using this technique to set slow beatings between the oscillators and leaving the fine tune knob alone. Hopefully Arturia can add some kind of scaling to the fine tune knob to make it more "Fine".

[BobTheDog]

Concerning autotune on my MB it doesn't seem too accurate, on the middle C I get:

Osc1 = -9.8 cents
Osc2 = -9.4 cents
Osc3 = 1.3 cents

So Osc1 and Osc2 are basically in tune with each other but out of tune with reality and Osc3.

I'd be interested to see other peoples results.

[F5D]

I managed to achieve the magnet like snap to the same frequency with the oscillators 1 and 2 also, when both were tuned far away from the detented center, so it must be something in the circuitry, not just the mechanical detents of the knobs. However, it does not happen always, but more often soon after running the auto tune. I also find that the tuning drifts after a while, so that it is actually easier to set this kind of slow beating sound with oscs 1 and 2, letting the fine tune of one of the oscs be in the detent spot, while the correct tuning of the other can be found outside of the detented spot. Run the auto tune and you are dealing with the detents again.

[BobTheDog]

Thats interesting, I must admit I haven't heard the snap using the mod matrix approach, maybe I have been lucky. Why don;t you give a try and see.

One thing I have noticed is that an oscillator can change tuning as if they have a square wave modulating them, haven't got to the bottom of this and it only seems to happen in the first 30 minutes after power on.

[F5D]

One thing I have noticed is that an oscillator can change tuning as if they have a square wave modulating them, haven't got to the bottom of this and it only seems to happen in the first 30 minutes after power on.

This could be also the same as I found interesting random pitch variation of the two oscillators that can be easily spotted by listening to the beating / phasing of two saw waves, but not by listening to 1 oscillator alone. It indeed sounds a little bit like square wave modulating, trying to compensate some voltage during warmup period. I believe the same can kick in after running the auto tune. Because I can hear this behaviour more often soon after running the auto tune, I think it still keeps working on the background even after the Tune text has gone away, and actually stops doing its thing after a few minutes.

Would be interesting to hear from Arturia about how long does the auto tune actually keep working, or should it be over after 3 seconds, when the text goes away too?

[BobTheDog]

I Just did a test, repeatedly autotuneing and checking the tune of OSC1, there are the tuning I got in cents middle C

-13
-7
-10
-9
-22
-9
-16
-15


As you can see a fair amount of variation, there must be something going wrong here.

[BobTheDog]

Managed to get the square wave type modulation tuning error using the matrix approach when the control is at 100% and the mod depth is set to 3, changing the mod depth to 5 and lowering the control value made it go away.

Using one OSC: https://soundcloud.com/bobthedog/mb-strange-osc

[F5D]

Did you check how the two oscillators tune in the repeated test in addition to just 1 osc? I have not measured the tunings of the oscillators other than listening the beating by ear. There are slight variations in tunings also between the two oscillators after each autotune, but if they both go such a large amount in the same direction, it is more difficult to hear.

[BobTheDog]

Osc 1 and osc 2 stay roughly in tune with the varying results, so both are off by nearly the same amount.

[F5D]

BobTheDog, your idea of using one of the macro knobs for osc fine tune is quite useful. I will probably set VCO2 fine for M1 always, if not needed for something else. Then, it can be quickly tweaked to get suitable beating, if the tuning tries to do its own thing. Btw, I am fine with the synth even if the tuning is a little bit wild as it is now. There are workarounds to deal with some of it, and it makes the synth sound more unique and organic. However, I still want to see what Arturia can do to improve the consistency of the auto tune and possibly explain why the oscillator frequencies sometimes just snap together when they are close, and if that could be disabled. I would much prefer freely drifting oscillator frequencies in that case, not trying to force sync them.

[DrAKS]

YES !!! Injection locking!

As a child in the 1970's I had several discrete NE 555's flashing their own separate LED's. Each NE555 had   different value peripheral
timing components but all the LED's ran in sync!

I wondered what the mechanism was back then , no one was interested enough to answer my question.

This sync was absent when the chips  had their power supply isolated from one another .

I should have tried inserting a blocking diode at various points.