From Brian Willoughby Sent Fri, Jan 4th 2019, 06:08
From Brian Willoughby Sent Fri, Jan 4th 2019, 06:08
Not all digital mixers max out at 0 dBFS. The ADC section of the = hardware certainly maxes out at 0 dBFS, as does the DAC, but the digital = mixer section can be programmed in many different ways. What happens to = the samples between ADC and DAC can vary a lot from one design to = another. The standard DSP (digital signal processor) instruction set and register = model builds in a default of 8 bits of headroom, which allows levels up = to +48 dB before clipping. This is the standard case for fixed-point = DSP. Of course, something needs to set the final output level below 0 = dBFS scale to avoid clipping in the DAC, but there are many places in = the signal path to handle that when mixing. Pro Tools has 16 bits of headroom, so they clip at +96 dB. Their early = DSP hardware was fixed point, but went beyond the default 8-bit headroom = to improve the performance for audio when mixing lots of channels. I = happen to find it fascinating how much effort went into the early Pro = Tools hardware DSP in order to get good performance. They certainly knew = what they were doing. Of course, things have changed multiple times = since then. I use the Metric Halo Labs interfaces for my mixing, and its faders go = to +10 dB for each channel, plus you can insert effects to increase = gain beyond that. Internally, the MobileIO DSP uses 40 to 80 bits per = sample, and thus there=E2=80=99s a lot of headroom. The MobileIO system = can be used for live recording, FOH, monitor mixing, mastering, or = studio mixing. The techniques for mixing successfully in MIO Console are = perhaps different than other digital or analog systems. I previously used the MOTU CueMix system, and it seems to be designed = very differently. All faders max out at 0 dBFS, and there doesn=E2=80=99t = seem to be any headroom built in at all. The techniques for mixing = within CueMix will be very different from Pro Tools or MIO Console. My 'calibration' technique is a little weird, perhaps. I like to find = out where a given piece of musical gear clips. That will be its maximum = output level under all settings. I then set the input level of my mixer = so that the red overload indicator lights up when the attached gear on = that channel is clipping. This way, there=E2=80=99s no additional = headroom being wasted, since typical analog electronics cannot output a = voltage any higher than their clipped level. Normally, the analog = musical gear is not clipping, so there=E2=80=99s a lot of internal = headroom. All of that headroom is then available to the ADC input. When = it=E2=80=99s possible to set things up using this technique, you never = have to worry about clipping the ADC. As long as you=E2=80=99re using = 24-bit digital, you should have nothing to worry about with regard to = the typical levels being much lower than clipping. Of course, there are all kinds of exceptions to this technique, since = noise or other problems may occur independently of the clipping level. Brian Willoughby On Jan 3, 2019, at 4:55 PM, John Sexton <xxxxxxx@xxxxx.xxx> wrote: > Echoing Maytag, using an audio interface as your "mixer" which many = including myself do, (which I call "headless") means no individual track = will clip until it crosses digital 0db, but if you say send a sine wave = directly from a modular VCO or something as a test tone, to every = channel with the goal of hitting -1db let's say, in order to set all = your gains, when you go to sum everything in your DAW in a project with = 24 channels of audio, you won't have any headroom for anything, since = there is no equivalent of the analog mixing console "pushing it into the = red" concept at all, since it just sounds like ear splitting heavy metal = fax machines when you get digital clipping. There is no soft, = overdriven, or saturated form of digital clipping. Everything above 0db = is a problem.=20 >=20 > This is why many people do some variation on "K-Metering" or K-14 or = whatever other branded forms exist out there. You don't really need a = plugin like: https://www.meterplugs.com/kmeter# if you understand the = concept, and don't worry about how the meters look in your DAW, all low = and stuff. The idea is that modern audio interfaces have plenty of = headroom, and high sample rates, so you don't need to max out the levels = in order to get a good signal to noise ratio on every recorded track = like you did with analog consoles and multitrack tape, so you decide, = basically arbitrarily, how much "push it into the red" virtual headroom = you want your virtual mixer to have in the digital domain, and you might = want to analyze how many tracks your finished DAW productions typically = have, so you may want to individually adjust this up or down, but the = typical "starting point" you might be looking for is -14db below 0db. = Send some consistent tone to every channel, and get the hardware meter = and the DAW meter to hopefully read the same -14db and then voila, = you're "calibrated" so to speak. I know guys using -12db or -10db or = -16db as their starting point standard. Thing is, the second you start = sending any real world signals like a Eurorack modular, or a passive = bass guitar, going to an active direct box, you'll have to adjust all = your trim levels for each individual signal all over again, since no 2 = sources are going to produce the same decibels consistently. Heck, one = synth will bounce radically different levels, just set to different = patches or knob settings. All your initial exercise will do, is ensure = none of your 3 MOTU devices have failed channels, or are not way out of = sync with each other, more than anything else.=20 >=20 > On Wed, Jan 2, 2019 at 9:04 PM DJ Maytag <xxxxxxxx@xxxxxxxx.xxx> = wrote: >> IIRC, the MOTU mixer is digital, so max volume is 0, and there really = isn=E2=80=99t a unity gain setting.=20 >> On Wed, Jan 2, 2019 at 5:35 PM Boniforti Flavio = <xxxxxxxxx.x@xxxxx.xxx> wrote: >> Got it! >> I'll look it up on my CueMix, but seems that it hasn't that unity = gain position like the A&H mixer: >>=20 >> http://cdn-data.motu.com/site/images/cuemix-fx/mix_large.jpg >>=20 >> F.=20 >>=20 >> Quincas Moreira <xxxxxxx@xxxxx.xxx> schrieb am Mi., 2. Jan. 2019, = 22:13: >>> I don't know about the MOTU, but on most boards like the A&H I own = it is clearly labeled. It's the center of the area with denser line = arrangement on the graphics : = https://articulo.mercadolibre.com.mx/MLM-630347460-mezclador-allen-heath-z= ed-14-_JM?matt_tool=3D10036016&matt_word&gclid=3DCj0KCQiA37HhBRC8ARIsAPWoO= 0yLyxFNLCjKtSapEqGZfZfHV1k3sc8lWCBOWUslm70xscmTHVYyytoaAlhPEALw_wcB&quanti= ty=3D1 >>>=20 >>> On Wed, Jan 2, 2019 at 3:07 PM Boniforti Flavio = <xxxxxxxxx.x@xxxxx.xxx> wrote: >>>> I hope I won't mix moisture ;-) >>>> I do have a "virtual" mixer - MOTU's CueMix.... What would be the = unity gain position anyway? >>>> F.=20 >>>>=20