Re: [AH] "calibrating" my audio mixer?

From Brian Willoughby
Sent Thu, Dec 27th 2018, 01:39

Ha!

Most of the time, Andrew is right. It has been my experience that -18 =
dBFS is a good target, although I place my peaks there, not sustained =
sounds. But that fact is that this is hardly a standard that anyone can =
rely upon. Sometimes you have to go to great pains to calibrate the =
meters so that 0 dBFS actually reflects any sort of known reference =
level. Bob Katz goes over the steps in his book.

At the other end of the spectrum, many analog synths have terrible =
performance with the master volume at 12 o=E2=80=99clock. Not all are =
bad there. In fact, some might work best there. But at least a few =
synths require maximum volume if you=E2=80=99re going to get decent =
signal levels out. It=E2=80=99s also far more repeatable to aim for max =
volume than to aim for 12 o-clock, unless there is a detent there (and =
even then there can be variation). Again, there is no standard rule that =
we can rely upon.

You really have to get to know your gear.

Brian Willoughby


On Dec 26, 2018, at 5:32 PM, laurie <xxxxxx@xxxxxxxxxx.xxx> wrote:
>  and on planet earth ?
> :)
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> ---- On Wed, 26 Dec 2018 19:25:51 -0600 Andrew Horton =
<xxxxxx.xxxxxx@xxxxx.xxx> wrote ----
> Set all synth self volumes to maximum for best s/n and gain. Set =
sustained/average levels to -18 - Peaks can go higher. Most ADC=E2=80=99s =
are calibrated so that -18dbfs =3D =E2=80=9Canalog zero=E2=80=9D on a =
traditional VU Meter and are designed to sound and operate best at -18.=20=

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> Sent from my iPhone=20
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> > On Dec 26, 2018, at 7:14 PM, Brian Willoughby =
<xxxxxx@xxxxxxxxxxxx.xxx> wrote:=20
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> > This is a tough question to answer, partly because I think there are =
two aspects to the answer.=20
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> > 1) Avoid distortion from clipping; maximize signal-to-noise.=20
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> > 2) Postpone adjustments for loudness until the final mixing stage. =
There=E2=80=99s a difference between optimizing per-channel S/N and =
adjusting the loudness for a good mix. Don=E2=80=99t confuse the two by =
trying to handle them at the same time with a single control.=20
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> > On the first topic, I would hope that every synth/drum machine would =
have been designed so that it will not clip its own mixing stages. =
However, we cannot rely on this because many audio circuits over the =
years, even from well-respected brands, have included design mistakes =
that are less than optimal. Therefore, it seems that you will have to =
determine whether each of your synths/drum machines clip internally when =
the master volume is at maximum, and if so then you=E2=80=99ll have to =
discover the amount that the volume needs to be reduced until there is =
no distortion (unless, of course, this distortion is part of the sound =
that you=E2=80=99re trying to record).=20
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> > Part two is whether your =E2=80=9Cmixer" input can handle the =
maximum volume of each synth/drum machine. In my experience with the =
MOTU 896HD, the input levels can only be boosted, not attenuated, so =
there were many recording situations where I needed to reduce the output =
level on the sending device because it was otherwise too strong for the =
896HD to handle. Analog mixers tend to have switchable pads, and my =
Metric Halo Labs interfaces have programmable Trim that can reduce =
excessive input levels. If you don=E2=80=99t have this option, and if =
any of your synths/drum machines are =E2=80=9Ctoo hot,=E2=80=9D then =
you=E2=80=99ll need to reduce the master volume.=20
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> > Personally, even when I have the option for Padding Line level =
inputs, I rarely boost a device=E2=80=99s output level if it means that =
the mixer will need to be Padded. Those pad resistors can add a little =
noise, so it=E2=80=99s better to reduce the send level so that the Pad =
can be disengaged. The result will be cleaner. Of course, it=E2=80=99s =
generally true that more signal level on a cable is better for S/N, but =
once you=E2=80=99ve reached the limits of a +4 dBu Line Level input =
(which is about +26 dBu!), then you already have more than enough S/N. =
Boosting above this, to the point where you need Pad resistors, is not =
going to improve anything at all.=20
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> > Finally, you don=E2=80=99t want to sacrifice the signal-to-noise =
performance of an individual channel by turning it down to adjust its =
loudness to match anything else. Psychoacoustics research tells us that =
there is a difference between the level of signal as measured by =
voltages and meters versus the loudness perceived by the human hearing =
system. Since noise gets worse as you turn things down, I recommend =
avoiding the temptation to match loudness between synths/drum machines, =
and just maximize the channel S/N. Once you have a mixer full of =
channels that have minimal noise, you can mix based on loudness and =
retain the option of making some devices louder than others during part =
of a song, while other devices might be louder in other parts of the =
song.=20
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> > Looking at the above from a different point of view: If you=E2=80=99ve=
 already maximized S/N for every channel, then you no longer have the =
option of turning anything up. Thus, balancing loudness means turning =
some things down, which just makes the noise worse. Loudness adjustments =
should be a creative step, possibly automated, and certainly dynamically =
changing during the progression of a piece of music.=20
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> > Another issue to keep in mind here is that the presets on any synth =
or drum machine will vary drastically from one selection to another. If =
you try to adjust levels to match loudness across devices, that balance =
will be lost as soon as you select a different sound or a different bank =
of sounds on any one or more synths/drum machines. Instead, if you =
adjust for maximum signal-to-noise, as described above, then your mixing =
process will be most successful at matching (or mismatching!) loudness, =
as appropriate for the art.=20
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> > Bottom line: These questions are all part of the general topic of =
=E2=80=9Cgain staging=E2=80=9D - which is very important in a recording =
studio. There=E2=80=99s a lot to learn. I recommend Bob Katz=E2=80=99 =
=E2=80=9CMastering Audio: the art and the science=E2=80=9D as one =
starting point. It won=E2=80=99t cover all aspects of recording studio =
gain staging, but it certainly covers all of the technical basics that =
you=E2=80=99ll need. If anything, Bob=E2=80=99s book is probably more =
appropriate for your situation, where you have a digital MOTU interface.=20=

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> > Brian Willoughby