Motu UltraLite-mk4 technical measurements (DAC only)

Discussion in 'Source Measurements' started by atomicbob, Jun 5, 2020.

  1. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    13,097
    Dislikes Received:
    4
    Trophy Points:
    113
    Location:
    On planet
    I just threatened to turn up the Suck Knob if they didn't give me at least that 15 paltry minutes. Start the show at 50% suck and then it goes up or down depending on many factors.

    Mackie Suck Knob.png
     
    Lyander, sphinxvc, Dzerh and 2 others like this.
  2. Serious

    Serious Inquisitive Frequency Response Plot

    Friend BWC MZR
    Joined:
    Sep 28, 2015
    Likes Received:
    1,823
    Dislikes Received:
    0
    Trophy Points:
    113
    Location:
    near Munich, Germany
    We do have building codes and I just tried to find the relevant part of it... seems that the only real guideline is that there has to be sufficient window space. No visible ventilation along the ceiling either, for example. In fact even the office I am in now does not seem to have any ventilation, but as I said it does have air conditioning.
    It's possible the 2500ppm figure is wrong. I just googled the model they were using and looked at its specifications, but maybe I had the wrong one. There is a lot of research on the topic. According to some of it the median CO2 value in a classroom could be higher than 1500ppm already. Depends a lot on the school, with some schools in Switzerland supposedly keeping CO2 concentration below 600ppm at all times!

    We always had to open the windows between class and when they exceeded 2500ppm. That was the ventilation system here lol.
    In the large lecture halls at the university they of course have real ventilation, but to be honest in many lecture halls the air quality seemed subjectively even worse than the classrooms in school. Could also be subjective due to there being no windows in many of them.

    You are right, it kind of looked different in my head at the time. And I should have mentioned that the two parts of my post weren't related, with the first one being a reply to your post specifically and the 2nd one being a reply to the thread in general.
    Already mentioned it in my profile post, but I'm glad to hear this from you. I thought I was being too picky. But again, how much does it matter when even normally spoken word masks the ca 20dBA noise (see the U47 file I posted here). At least I can't hear it anymore when he starts speaking. I probably care too much, otherwise I wouldn't have the mics I have, but maybe I shouldn't.

    Well, it seems that as per atomicbob signals near or at 0dBFS can exceed power supply limits for the analog stage, clipping it. That it's not an issue is your opinion, which may not be shared by the engineers. Everyone can form their own opinion with the two files I posted, which emulate this behaviour.
    Just thinking out loud here. To be honest I do think it's an issue, but it's so slight that it doesn't matter. My guess is the engineers knew about it and decided to leave it as is. Or maybe it's just unit to unit variance causing this one to clip, while others would be fine?
     
    Last edited: Jun 24, 2020
  3. purr1n

    purr1n Finding his inner redneck

    Staff Member Friend BWC
    Joined:
    Sep 24, 2015
    Likes Received:
    61,044
    Dislikes Received:
    107
    Trophy Points:
    113
    Location:
    Antarctica
    If it's an issue, then set the master trim to -1db. All this has been discussed prior.

    Engineers listen to amps with 77db SINAD and speakers with worse. Trust me, audio engineers don't give a shit about this stuff. The ones doing the mixing and mastering will at most say something along the lines that they think a tweeter is blown or they they hated it when the JBLs were replaced with Genelecs. The ones that put the shit together will worry more about whether they have enough power for the subs or how much to treat the room for a given budget. No professional cares about -90db spurae at 0dbFS. Worrying about this stuff is the realm of Audio Scientology.
     
    Last edited: Jun 24, 2020
  4. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    13,097
    Dislikes Received:
    4
    Trophy Points:
    113
    Location:
    On planet
    My measurements demonstrate harmonic content at -58 dBFS when presented with a 0 dBFS 1000 Hz sine stimulus. If the stimulus is lowered to -0.2 dBFS the resulting harmonic content is at -80 dBFS. When using either -0.5 or -1.0 dBFS stimulus the harmonic content drops to -110 dBFS. All this suggests the sine signal is just beginning to touch the power supply rails at 0 dBFS.

    This type of behavior is not limited to Motu. Plenty of other DACs have issues close to 0 dBFS of one kind or another. I co-presented on this topic to AES PNW as can be found here:
    http://www.aes-media.org/sections/pnw/pnwrecaps/2018/oct2018/
    You can download my presentation deck which contains numerous slides showing signal going into a DAC and the DAC output recorded on a high resolution oscilloscope. One DAC was particularly egregious in its behavior near 0 dBFS.

    The intent of demonstrating UltraLite-mk4 0 dBFS behavior was to help users optimize performance.
    SUMMARY: SET THE OUTPUT TRIM TO -1 dBFS and BEST PERFORMANCE is ACHIEVED.
     
  5. Psalmanazar

    Psalmanazar Most improved member; A+

    Slaytanic Cliff Clavin
    Joined:
    Sep 27, 2015
    Likes Received:
    4,018
    Dislikes Received:
    128
    Trophy Points:
    113
    Line level is +4 dbu. The MOTUs output up to +20 dbu for headroom more than a ton of other converters in their price range. Almost everyone with one will be attenuating digitally, which is done inside the ESS Sabre chip itself. This measures better than most pots and resistors according to MOTU themselves. If you’re outputting to speakers at +20 dbu, you’re going to be attenuating, deaf, or getting the police called on you.

    For all of your complaints @Serious , the MOTU power supplies are much more robust than RME and Apogee Symphony 1 ime. If the power supply or power parts of your fail, you get very digusting and offensive artifacts. This is where the RME hardware that’s not PCI-E cards falls down horribly in real world use discounting sonics. Durability.

    Your M2/M4 doesn’t even have a power supply and uses a cheap pot like every other cheap interface. It’s hard to get consistent levels and settings from an audio pot. That’s why all the mastering gear has switches and resistors. Drawmer uses a quad tracked pot and has some durability issues but free replacements and Coleman a military spec one in their pro products for better level matching. A cheap interface or converter can’t afford to use those.
     
    Last edited: Jun 24, 2020
    Koth Ganesh likes this.
  6. Armaegis

    Armaegis Friend

    Friend BWC
    Joined:
    Sep 27, 2015
    Likes Received:
    4,099
    Dislikes Received:
    2
    Trophy Points:
    113
    Location:
    Winnipeg
    Our ambient CO2 levels here are typically 450-550ppm (medium size low density town, not much industry). General guidelines for target levels are at "ambient+400 ppm", so rounding up we say we aim for 1000 ppm. Below this we consider it over-ventilating and wasting energy on heating or cooling. I don't remember the exact values, but on a standard 3-level monitoring system the set point is around 1500 which should kick up the fan speeds. Somewhere in the early 2000's it will max the fans and send a warning to the control station. Somewhere between 2500-3000 is the actual alarm.

    "Sufficient window space" sounds more like a building code requirement for emergency egress, such as if your doorways are blocked by fire.

    "No visible ventilation" ?? That's new to me. I feel like it's more of a design requirement and not a building code. It's common here to have open ceiling returns, which treat the entire ceiling space (commonly a drop ceiling) as a return duct. In such a case you'd either have ducted supply also in the ceiling, or possibly the wall or floor. In your case, I'd assume there would still be open return on the ceiling (maybe not visible, but hidden behind light fixtures or the panels are perforated), and then your air supply would be on the floor. That would use natural rising convection to help circulate air in the room.

    Anyhow, I digress. So how about that MOTU eh? It sure has... a lot of... knobs on it, and stuff :oops:
     
  7. Serious

    Serious Inquisitive Frequency Response Plot

    Friend BWC MZR
    Joined:
    Sep 28, 2015
    Likes Received:
    1,823
    Dislikes Received:
    0
    Trophy Points:
    113
    Location:
    near Munich, Germany
    I just checked back on this and my MOTU M4 does seem to use a digital volume control. 1dB stepped for most of the range on the inputs and outputs, 0.5dB stepped on the mixer. The very low end of the range has 4dB steps it seems and the very top has 0.5dB steps. No channel inbalance at all.

    @Armaegis I'm not sure what to say other than... HVAC systems are not nearly as common in Europe as they are in NA. I still sort of doubt the school had active ventilation, but I honestly don't remember. At work only some rooms have ventilation, although as of this year all of them have air conditioning. At university many rooms are connected to large HVAC systems, while some smaller rooms only have smaller AC units. Some small rooms don't have either.
     
    Psalmanazar likes this.
  8. wadec22

    wadec22 Facebook Friend

    Contributor
    Joined:
    Sep 28, 2018
    Likes Received:
    115
    Dislikes Received:
    0
    Trophy Points:
    33
    Location:
    USA
    @Psalmanazar for attentuating is there a benefit to using something like the SPL 2Control or would you stick with the digital implementation/pot on the unit itself?
     
  9. Psalmanazar

    Psalmanazar Most improved member; A+

    Slaytanic Cliff Clavin
    Joined:
    Sep 27, 2015
    Likes Received:
    4,018
    Dislikes Received:
    128
    Trophy Points:
    113
    It’s done floating point in the ESS DAC itself. The on the chip and in daw (If you use current Reaper, Pro Tools, or Cubase) floating point attenuation are definitely the best digital volume controls I’ve heard (They kill the digital volume control ics ime) but a real knob is still useful and can prevent digital errors from blowing your tweeters. The motu has a digital volume control ic on input but the ad is warmer than the da by design. I don’t even think it would matter that much given the dialed in tone of the adc.

    A good pre amp or monitor controller is another few hundred bucks and will be more colored (Drawmer, Dangerous, Grace) if active and a pot won’t have great stereo tracking at the extremes unless you get one of those mil spec Coleman units. Do not get cheap active like the current Mackie and Presonus pres. They are bad sounding and noisy and smear the sound of anything better than Focusrite Scarlet or Steinberg 2 channel units.

    I use the MOTU digital volume control and Klanghelm vumt deluxe plugin (best digital vu meter around) for mono, m/s, and channel swapping.

    Search for @atomicbob posts. He is right about this stuff and has great info!

    Oh and do not use your daw / Media player as a volume controller and turn it down a ton and drive your amps hard. Recipe for disaster with amp distortion and digital errors and overloads.
     
    wadec22 and Thad E Ginathom like this.

Share This Page