Gain aGain

that’s where I’m coming from, if there’s a way to get a better snapshot of your live inputs I may be more inclined to just sample into the OT to capture short ideas rather than hooking up other recording options

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yup same for me with ideas I have in mind recently I will have to deal with that too, and I think OT still be best candidate to start directly to shape something from recorded material…

in this analytics way of thinking I would give here my thoughts based on OT MK2 of course…
Practically sure to have some things to write next week. Sticked note on my fridge to come back on that thread :wink:

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Yeah off course it’s a particular test with exactly the same signal at 0db.

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I’ve always found to get the sampled level back I can always get there within the +63 via amp page, I think you might be right about it being attenuation rather than gain there. I just record healthy signals then mix by cutting rather than boosting, Then I can always bring the overall level up a decent amount at the end without clipping. Failing all else if I can’t get decent levels from something (which is rare) I stick a pre on it

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Indeed, the OT clearly works well on the whole for what it’s intended to do, but I’m on page 1 wrt capturing the sample at its best, useful info like this is for page 2 and so on :wink: … the gain attribute on the sample settings page defaults to +12 for captures, but that’s for playback … if you want to take a nice captured sample out via USB disk mode I think i’d rather do fine level tinkering in other software, but getting the best signal possible will be a bonus, thus the focus on the Mixer Gain and input attenuation at the moment, first things first, especially wrt those pesky LEDs

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Ah, i think i have discovered that there’s been a bit of a prior misunderstanding, possibly on my part and it’s been perpetuated …

I tried Setting the Gain to 0 on the mixer to see how far i could push the DE, it could go way beyond the 1/4 scale captures you’d see if the inputs were categorically being lowered by -12dB … but not far enough, the VCA seemed to level off after about 7>8 and it was maybe 2/3rds or more full-scale on the OT and the shape was good/clean (red inputs)

So i stacked up some 0dB sine samples on three tracks on the AR and that produces a punchy sine level to push into the OT at Gain level 0 (i was able to get closer to full scale and could eclipse it by adding more stacked SINs introducing distortions to the waveform)

This is the result … it’s a single harmonic, no clipping and it’s clearly not attenuated by -12dB (i.e. the sample)

Applying Gain will introduce a shape change as the Sin is clipped at the peaks and troughs, so it’s absolutely contradicting what i’ve dropped into discussions from time to time based on the assumptions put out in the older thread experiments

That’s not to say i have everything understood, it’s just clear that the previous assertions are wrong - ps - fwiw, this signal was also way way into the red, but it’s not distorted (or Gained)

so i need to rethink input metering and using the OT as a capture device, it’s better placed than i assumed before for some of my usage cases, that’s not to say the way jot’s set up by default isn’t best for typical usage scenarios, but it ought to be possible to capture decent samples with a bit of prior configuration especially at source

I also think that Gain in the Mixer IS gain !

It’d be easier to test all this out with proper signal generating equipment, but i’m satisfied a few mistruths have been addressed, albeit posed originally as questions (and fuelled by the comments in the manual about applying automatic +!2dB gain on captured material)

I’m still not convinced there isn’t more info to uncover wrt all of this, but i thought this was significant in terms of my understanding of what was occurring

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The manual’s wording is pretty unambiguous but I wonder if what’s actually going on is that the LED metering is set up to give about 12db headroom, and rather than being padded -12db like it describes the reality is that the LEDs go red at -12dbfs s if you follow their directions for setting input levels and get it so it’ peaking just below red, you’ll end up with an audio file that has 12db of headroom.

It wouldn’t make any sense for the manual to be written the way it is in that case, but it WOULD explain a lot of the unexpected gainstaging behavior.

EDIT: after work this afternoon I’ll do some experiments focusing on thru machines.

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Has elektron ever stated why there is no digital FS peak metering for the inputs?

I am having trouble grasping the implications of htese findings… These apply to OT mk I? So on the mk I, redlining the input meters is the way to go?

fwiw I think that the whole -12dB ”pad” was a design mistake and we’d all be better off if such a safeguard were never implemented in the first place… Digital audio fundamentals are not rocket science, if some dweebo clips the mixbus by overly hot signals its not fair the rest of us need to suffer from it too… Even MPCs clip the internal mixbus if you don’t mind your track levels, and most users learn to get on with it jus fine.

Does anyone happen to know the internal bitdepth of the OT mixbus? 32bit float? 24bit fixed-point? other?

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I only have a MKi. It’s more nuanced than some of us maybe thought before, but it’s clear you can in some circumstances (without gain or attenuation) get good recordings when it’s solid red (or even if you need to use gain obviously) and there’s not necessarily massive level reduction at the point of capture either, so you’re good to go for quick and dirty sampling with decent levels (without resorting to edit boosts etc) - makes it a bit more usable, but clearly there’s conflicting forum chat about the significance of hitting red at all - because i’d always thought the gain reduction was a given, I never sought to maximise the digital levels the way you might in an audio editor for best signal to noise (it’s always easier to attenuate than to correct for low gain captures)

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In general for setting levels I’ve used the noise gate and set it around -14db and adjusted source until it’s peaks pop through, and I’ve looked at the waveform to in the editor to analyze its height(amplitude). I’m always a bit concerned with how far I push it (red meters) to reach what seems still an OK level so even though it sounds good, I drop it back a bit…

A general concern has been about not being able to record hot signals into the OT, I’m always sampling gear with their volume knobs most of the way up without clipping…

My settings with high track levels may work out for me because most all my samples are captured by the OT, I don’t know if I used pre recorded samples especially normalized if it will still sound OK. I also don’t use volume boosting fx…

I believe track level default is 108, so it seems that should be fine?
Lately I’ve been reconfiguring for track levels around 100, because I often directly cue the inputs which then output to cues at a level equivalent to 100 on mixer direct…

I’ll occasionally load a regular sample and I’ve noticed on one going through a few fx that affected volume, I had to drop the track level to around 50 to match my live sources…

This may be why I feel I get better sampling mix results, because everything I’m mixing is audio passed through the OT or sampled by the OT, I’m not using pre recorded loud samples to have to mix around… And again this may be why I can get away with high levels everywhere…
@avantronica, I know your main focus is the input levels, but I have to bring outputs back into this in case it’s possible to make too hot of recordings that cause us to have to drop track levels…

If normalized samples clip the OT when using high track levels, and noisebuddy and others have experienced muddy sound, can we drop the master instead of the track levels?
I wonder if you adjust track level, master track level, master level, sample gain, amp vol, if they each have a separate discrete effect on headroom? Is it the sum total of all of them that will end up clipping? Might amp vol and sample gain have a discrete affect but levels be additive?

Be interesting to find out how these all affect each other, and to bring back to topic what would be a desirable recording level to not have to decrease anything on the output stage.
In other words, does a recording start getting too hot for overall summing before clipping occurs, causing us to drop output stage parameters when we could have captured a lower, more desirable strength recording that mixes well with default output settings?

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A tad more on the same tangent:
Perhaps you can make and playback a recording pushed into the red without clipping, but if you play 8 recordings that have hit red it will clip? So the meters would be telling us hey, if you keep this up with the rest of the tracks you’ll be clipping and have to turn down output stages?

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Other tests with a 0 db Sine wave on 8 tracks. Track Level and Master Level limits to avoid clipping :
90 with Master Level at 0
108 with Master Level at - 11
127 with Master Level at - 19

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Fascinating… could we perhaps be able to calculate the overall headroom with these parameters? If you can compensate the teack levels with the master fader, it would suggest a hard limit instead of a teack-by-track basis?

Another test with that 0db Sine :
Send Cue Out to Input AB with 2 cables.
Red light with
Cue = 127, Master Cue = 16, Gain =0

Checked Input with Noise Gate :
Red light is between - 12.3 db and - 11.2 db

Red light just before clipping with
Cue = 127, Master Cue = 63, gain = 3
(between - 3.3 and - 2.2 db)

Recorded. No clipping. The sine is near 0db

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I feel like we’re getting closer to something…
If we actually could come up with a chart and equations where you could take your 8 tracks sample db levels, apply the attenuation equations for each parameter, and calculate the usage of available headroom, we should win the Octatrack Nobel Gain Prize…

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Thanks sezare, those are important results confirming master level can compensate for track clipping, and that track level and master level have a combined affect on headroom, but not by the same value scaling…

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@Open_Mike Check results above. I could really increase Master Cue (and gain) before clipping.
Red light : between - 12.3 db - 11.2 db
Clipping : between - 3.3 db - 2.2 db

I don’t know if noise gate db values are correct.
If I set my sine recording to 12.5 db instead of 12 db in Attibutes, clipping. So I think I’m very close to 0db.

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For clarification to interpret your results,
Is your original 0db sine wave sample set to 0db gain in the attributes?
And it’s the recording of that sine that is set to +12db?

If so I think it would be interesting to compare sign waves with the +12db setting, even if we have to drop the original level, as to better compare the parameter values with those used for a recorded sample…

Yep, yep. 0riginal 0db. Recorded +12 db.
Waves are almost the same, 0db, but recording is +12 db louder, because of Attributes.

I upload my original sample, I found useful for level tests and clic tests (perfect loop at 120 bpm), and less anoying than 1000 Hz sine ! Right clic for download on windows.

SINE_256hz_2s_0db

SINE Recorded, peak at - 0.09 db

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Ok, I just did some tests on my MKI and the results were not what I expected, and I think they illustrate some interesting things.

For a test signal, I used Reaper’s built in tone generator, fed through an oscilloscope plugin, and then out a pair of channels on a Black Lion Audio modded Digi002.

To calibrate, I fed the outputs back in to a pair of line inputs (operating at +4db) and made sure that the direct loop was as close to unity as I could get it. In the end, I settled on the test tone at -2dbfs (the hottest I could get it without clipping the inputs) and added .399db of makeup gain on the input to correct for a bit of signal loss (basically setting it by eye so the oscilloscope on the test tone channel pre-output visually matched the oscilloscope on the input).

After that, I patched the test tone output to inputs A and B on my Octatrack, and the main outputs back into Reaper. I started a new project, set it up to record A and B into record buffer 1 and simultaneously play back record buffer 1 through the main outs. I turned timestretch off, but otherwise started with the OT defaults.

With a -2dbfs signal on the inputs, the output was hard clipped at just above -12db:

In the OT audio editor, the recording was digitally clipping at 0dbfs:

Next, I turned the mixer level for in AB to -32 to see if that kept the signal from clipping (which would mean that the level controls in the mixer were actually adjusting the input gain in the analog domain, pre ADC). I didn’t expect to see any change in the clipping, and there wasn’t any, which means that boosting and cutting the input level in the mixer is happening in the digital domain, between the ADC and the record buffer. The signal level had been lowered digitally, but the clipping was identical:

Next, I returned the mixer settings to their defaults and reduced the level of the tone generator until the output from the OT was as close to clipping as it could get without actually clipping. I ended up with the test tone set to -8dbfs. With the OT’s gainstaging at default settings, the output was approximately 4db lower than the input:

The input LEDs were still pinned in the red, but the audio in the record buffer wasn’t clipped:

Next, I moved on to the AMP page, and this is where I got my most surprising result. With the test tone still at -8dbfs and the mixer level for he inputs at 0, increasing the level on the AMP page to +1 or +2 started to clip the signal right away. By the time it was up to +12, the output was clipped heavily, and was still peaking at just over -12db:

As far as I can deduce from this, the OT’s signal path is not floating point, which means it’s possible to clip it internally! I have no idea (and no clue how it would be possible to test) what the internal signal path is like, whether it’s all fixed point or whether individual processes are done in floating point and then dithered back to 24 bit, but I think it’s pretty safe to say that at least some parts of the internal signal path are fixed point and can be clipped. The takeaway here is that increasing the volume on the amp page (or, presumably, with effects) can digitally clip - it’s not like a modern DAW where everything is floating point and you have essentially unlimited internal headroom. This is a big deal in terms of how you approach gainstaging.

Next, to see if the track level control could also clip the signal path, I returned all of the track parameters to their defaults again, and then turned up the track level. What I ended up with was just shy of unity gain when the track level was all the way up to 127, which suggests that track level is cut-only. However, because the record buffer’s Gain attribute was set to the default of +12 for all tests, track level at 127 presumably corresponds to 12db below unity gain).

Default OT settings with test tone at -8dbfs and playback track level at 127:

Next, I went to the settings menu an adjusted the gate threshold to the highest setting that would open on both channels with the tone generator still at -8dbfs. The highest I could get it was -4.5, although input A wuld still pass with it set at -3.3 (so either my interface’s outputs aren’t matched as well as I’d like or the OT’s inputs aren’t). At any rate, the gate settings are pretty coarse but in this test, a gate threshold of -4.5 roughly corresponded to an input level of -8dbfs, which more or less corresponds to just below clipping the input. Obviously this is pretty far from lab conditions but since you’d never want to drive the inputs hot enough to reach 0dbfs anyway, it’s still accurate enough to be instructive, if only because it shows that the gate threshold doesn’t necessarily correspond to a decibel value (or if it does, it’s calibrated quite differently than the line outs on my interface).

Next, I adjusted the tone generator’s level and watched the input LEDs, to find out where the transition from orange to red happens. First, what I noticed is that there are 5 distinct colors: green, yellow, light orange, dark orange, and red - if you gradually increase the input level you can easily see where the LED flips over from one color to the next - it’s not a gradual transition. The other thing I noticed is that the threshold between one color and the next is pretty inconsistent. I did a bunch of slow level changing and what I found was that if you start in the red and decrease the level, the transition from red to orange is much lower than if you start low and increase the level until you go into the red. In my tests, if you start low and push the input level up at the source, it will hit the red somwhere between roughly -16db and -13db, but if you start on full and lower the input level it willl go from red to orange somewhere between roughly -18db and -22db! Sufce it to say, the LEDs are a rough guide at best, and in either direction the level where they were pinned in the red was at least 4-5db below clipping.

Just to see, I set the test tone to -20db and adjusted the OT’s gate as before, to the highest threshold that still passed both channels. What I got was a threshold of 15.7. From this and the previous gate experiment, I’m speculating that the gate numbers are approximately input level in +4. Since my interface is (nominally, at least) operating at a +4 line level, perhaps the OT’s inputs are calibrated to a nonstandard +0db line level, which would be a reasonable way for Elektron to assure that they worked acceptably with both +4 and -10 equipment.

Finally, I returned the OT to its default gainstaging once more, returned my test tone to -8dbfs (which according to my tests corresponded to just below 0dbfs in the record buffer) and increased the master level in the OT mixer until I achieved unity gain, which happened at +12.

Soo, that’s a whole lot of information that may or may not be useful, but my main takeaways are:

  • A -8dbfs signal at +4 line level corresponds to 0dbfs (without clipping) at the OT’s ADC. Where the OT’s -12db pad falls in this equation I don’t know.
  • A gate threshold of -4.5 corresponds to just about the hottest signal that you can safely record into the OT without clipping
  • It is possible to digitally clip the OT’s internal signal path using the AMP level, and therefore AMP level should be used for cutting more than boosting and is the first thing to check if a signal is clipping but the inputs still have headroom to spare.
  • From the OT default settings, increasing a track’s level to 127 should result in unity gain.
  • From the default OT settings, increasing the master to +12 should also result in unity gain.
  • Track level appears to be cut-only. I was unable to clip a signal that was hitting 0dbfs in the track recorder by increasing the track level.
  • Don’t pay much attention to the LEDs and definitely don’t worry about keeping them in the green! Yellow to light orange is probably the sweet spot but even in the red there’s headroom to spare.

Another test I didn’t think of would be to set up something similar (a test tone on the OT inputs that was peaking at or just below gate threshold -4.5, recorded into a track buffer and played back from a flex machine), but put an analog pad of some kind (basically a resistor or pot, something that couldn’t distort) between the OT outputs and the audio interface inputs so that you could turn the OT mixer’s main level up all the way and see if it was possible to clip the OT’s DAC by running the mixer too hot. I assume it would clip but you never know.

Anyway, if anyone is up to try to replicate some of this on their setup I think it would be really interesting to see if the results were the same (and it would help eliminate the variables introduced by my interface maybe not being that accurately calibrated). Likewise, if anyone notices any glaring mistakes please point them out! Also, in some of the images the title on the return signal oscilloscope window might not match the test conditions I described for that image, but that’s because I forgot to rename it for a couple of them. Likewise the filenames don’t always match the test conditions exactly, but were close enough for me to keep track of what was what while I wrote this post.

Hope this helps! It definitely made me rethink my approach to OT gainstaging a lot.

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