Signal flow/gain staging diagram for Octatrack MKII

Elektron Gear Octatrack
#44

This just makes no sense in the digital domain though …
dB is just a means to express a ratio, it doesn’t have a meaning in terms of clipping a digital signal … you can’t have +15dB relative to 0dB … what is 0dB in this scheme ? what do the LEDs really indicate ?

In the digital domain you would express clipping in dBFS and that naturally ‘maxes out’ at 0 dBFS you can’t have definitive +ve values wrt clipping

I linked to an earlier thread on aspects of the gain structure, but that related to the Mk1 which has inputs which are not as broadly accommodating as those on the Mk2 which can handle higher input voltages

I think Elektron have designed the interface to prevent clipping in most usage scenarios, so the notional 0 points on bi-polar ‘gain’ encoders are there to keep you right if you have a full set of tracks running - but are these nodes really capable of adding gain or are they attenuating and which ones if any(presumably) do add gain (besides the process in the editor and at the inputs)

To capture a near FS signal into the Mk2 may require e.g. a hot eurorack signal - it should be easy after that to monitor whether the captured audio can be clipped if these waypoints are adding gain - and a hot signal will allow it to be tested for recording/thru/pickup machines etc - I should look at this on the Mk1, quite curious - I’ve chopped and changed my mind about what’s probably happening in the OT, but I am increasingly confident it is well configured and thought through by people who know what they’re doing

#45

The - 12db values in Machines column are not settings but theorical - 12db reduction for inputs / recordings.
As a compensation, Recordings have +12db in Attributes GAIN, and Thru needs Src / Playback page VOL set to +63 to add +12db for unity.

As @philtipping told me, it’s actually - 4db, corresponding to LEVEL 100 (from manual).
It’s a fixed value, you can’t access to it.

#46

Thanks MK7. Agree with take-aways, except +4 should be -4.

All values are dBV so are relative to 1 volt RMS (approx 2.8v pk-pk). My bad for lazy terminology :slight_smile: Feed a 15-16volt p-p signal into A, set mixer gain A/B to 0, DIR to 127, Main lev to 0, and main output shows clipping.

1 Like
#47

The electrical i/o specifications are in the respective Elektron user manuals, though they stipulate those in dBu, likely the same for the Mk2 manual - that reference scheme would make more sense to avoid potential confusion especially if folk read across both sources of info

#48

I corrected the +/- typo above, to avoid confusion when people just jump in and read those bullet points.

1 Like
#49

Fair enough for the input clip level, but in the context of this diagram, I wanted to show levels as they appear on screen, so plain old dBV (or just dB as Elektron themselves use in the manual and on some controls), seemed better to me.

I did read & appreciate the numerous threads on this subject, including the Gain aGain thread, but as mentioned in the first post couldn’t find any diagrams… so as I’m a ‘pictures guy’, thought I’d have a go :slight_smile:

If I missed it, apologies :slight_smile:
I got the impression you don’t have a signal generator as you mentioned using a hot eurorack signal to investigate clipping. I have a generator and scope so may be able to help if you need any tests doing.

2 Likes
#50

Very cool to see people figuring that stuff out!

Is there any chance to get the differences to OT Mk 1 described?

Thank you and cheers.

#51

Input levels on the Mk1s were giving people issues with hotter signals, so those inputs were upgraded along with the encoders/screen etc

The Mk1 Input handles +8dBu (5.5V peak to peak)
+17dBu for Mk2 (15.5V peak to peak)

sure sounds more convenient, but does that result in folk experiencing/perceiving samples which sound more underwhelming (due to loss of level relative to imported samples)

3 Likes
Can i input directly from Modular in to OTmkii?
#52

Concerning settings, same for MKI, AFAIK.
In the diagram, SRC is PLAYBACK, CUE+REC1 is CUE+RECAB…

#53

Yeah shoutout to the upgraded inputs, I was plugging modular straight in the other day, inputs red but no clipping :+1:

1 Like
#54

These figures don’t mean that you can feed a +17dBu signal into the MkII inputs and record/process it “as is” and expect not to clip the recordings. If you do so, you must turn the input gain down to adjust for anything that overshoots +4dBu. It means that the input stages can handle it without distorting beyond specs. I don’t see any reason for a loss of level compared to imported samples due to this hardware mod.

#55

Yesterday I played something too loud in inputs AB (MKI). Not working anymore, no leds! :scream:
Project change > working. Phew…

2 Likes
#56

hm ? fairly likely that the signal level here exceeded the nominal +4dBu and gain isn’t applied to the inputs by default iirc

I imagined (without the privilege of being able to try) the same signal sent simultaneously to the OT1 and OT2 (with same default settings) may be captured In the OT2 with more room to spare from 0dBFS - if I can nudge 0dBFS whilst recording sans gain into the OT1 then how does an OT2 cater for hotter signals ?!

#57

That’s what I found when increasing an input signal until the output clipped. My conclusion is in the notes: LEDs exhibit hysteresis, e.g. orange>>red when input signal goes above +10dBV, red>>orange when signal goes below +5dBV. Recordings clip at +15dBV. So if LEDs are red, signal may or may not be clipping, but keeping LEDs out of the red guarantees at least 5dBV headroom, maybe more depending on which way you adjust its level.

#58

turn the gain down…

#59

I think you’ve missed my point - if it can tackle notably hotter inputs than the OT1, then there must be more headroom left, it seems highly unusual that you’d need to turn the gain down on the OT2 - this is why I am speculating that the same signal sent to both will be further form 0dBFS on the OT2 - this seems like it could be problematic in its own right (for weaker signals) so perhaps all isn’t that straightforward, but the OT2 has to be able to handle hotter signals than the OT1 and as discussed above the OT1 can seemingly take an input up to FS (without gain/attenuation)

#60

Why? We’re talking about headroom, not levels… I believe there’s a misunderstanding due to imprecise wording in the documentation. When the OT2 documentation says:

Balanced audio inputs: Input level: +17 dBu peak Audio input impedance: 21 kΩ

that doesn’t mean that we need to input a +17dBu signal (5.48 volts RMS) to get a full-scale digital recording. What is omitted is the nominal input level, which we can logically suppose to be +4dBu like any studio grade balanced input should be.

In real life, this means that when we have our source VU meter (say it’s a mixer) indicate 0 VU, the source voltage will be +4dBu ( 1.23 volts RMS) and we can safely assume that this will result in a 0dBFS recording without clipping, which is what I experience.

The input circuit in the OT MkII is designed to handle a higher voltage, up to 13dB overshoot, but the gain must be turned down to prevent overloading the converters. When we turn the gain down, the leds follow. So, as I see it, the input amplifier is a DCA and sits before the converters (to be sure we should take a look at the actual circuit board). Otherwise a "gain " parameter on the inputs wouldn’t make much sense.

But that’s all guessing and not very helpful IMHO, really. The important part is matching source and input levels, the internal gain structure is pretty decently engineered with enough headroom for resonant filters, EQ’s and other goodies. All I need to know when sampling on my MkII is that when my digital mixer’s output level meter says -18dBFS I’m hitting the +4dBu ceiling at the analog outputs, and that means I’ll get 0dBFS samples with no clipping, given I have the OT settings to default. Your reference may vary, but it’s the same principle. And it’s exactly the same for the MkI, except that it has less headroom.

EDIT:

Sorry, but his doesn’t make sense at all. There’s no digital input on the OT, we’re in the analog domain. Much, much confusion…

1 Like
#61

Clearly there is some confusion here as you haven’t understood the logic in my posts. It’s already been explained above in any case by other people that the Ot is not waiting on nominal line level +4dBu to get a sweat on. I won’t waste our time to repeat it as it’s all above. You seem to be implicitly suggesting that the OT2 can’t take hotter signals than the OT1 which is certainly confusing given the literature. The notion relating to +4 dBu somehow being the level required to knock out a maximized almost clipped capture (without gain/attenuation) is IMHO misguided and contributing to this lingering confusion.

#64

v8 uploaded with corrected conclusion re. headroom due to the LED hysteresis. There’s at least 5dBV (not 10) headroom if they are not red, but this could be more depending on which direction you adjust the sig level. Bottom line is they seem to be a rough guide only; if they hit red you may get away with it, you may not. Maybe the phrase ‘let your ears be the judge’ is right after all :slight_smile:

1 Like
#65

I saw this too, some material was far more forgiving (example linked) whereas other regular sounds just clipped at red - it probably depends on the overall profile of the sound

1 Like