Someone was recently asking me if you can use the phase graph
in Smaart to compare to kick tone microphones and align them or basically
see what they're doing and and make judgments based on that and this is the
first time I've ever done it I've never tried it before so I had to test it out
and so I'll show you how I set that up and sort of what I've learned so far and
if some of you are experts at this and you do this all the time I hope you will
comment on this video and let me know what I'm doing wrong or what you do
instead so let me close a couple of things here I don't think I need this
open
we're gonna need to leave this open okay let me just make this window over here
smaller so I don't have to look at it all the time all right cool
so let me show you what I've got so over here in logic I'm playing to kick drum
recordings I've got a d12 e and a beta 91 a and I
know you can't hear what that sounds like right now so maybe after this I'll
make two recording samples and I'll post this on the video so you can hear the
samples so here's what those microphones look like we've got the AKG d12 e
and the shure beta 91 a I'm not sure how they're placed on this kick drum this is
a recording of a Counting Crows song that I got from some multitrack session
from a long time ago anyway probably the 91 a is inside the drum somewhere and
the d12 e is outside the drum somewhere but let's look at how we can start
comparing these so first of all and smart let's head over to the spectrum
view I'll hit play on this first guy so this is the
d12 eeee and this is the 91a and let's put them
in separate windows
I don't want to see this one I'm gonna stop that
I guess let's just look at look at them at the same window and let's turn this
down a little bit let's set this to like three seconds basically I just want to
compare before I look at a two channel measurement I want to look at the single
channel measurement and see how these guys align so I can see that around a
hundred and ten Hertz they're at the same level and both of them seem to have
a pretty good boost and emphasis here you know around 117 120 and then the
beta a 91 a that's what it is right yep the beta 91 a seems to have gentle or
roll-off at least back here we've still got a lot of information here and in the
d12 II there's a big cut here and then another boost and then kind of same
thing up here but let me just look at this low frequency information because
all this stuff up here is pretty low anyway
so that's pretty much all I can see with this single tin of measurement is how
these guys line up in level but I know that where they match and level
hopefully I'll get summation in those areas of as well I guess that could be a
creative question so on the input side of things a lot of times we're looking
at creative decisions and not necessarily scientific decisions right
so it's where things get a little bit murky in this discussion I guess but
those are the only first things I noticed when I'm looking at these okay
here's how their frequency responses compare in the low end so now let's look
at the thing I was really interested in looking at which is
the transfer function so I've got it set up so that in logic the D 12v is the
microphone signal and the beta 91a is the reference signal so I'm going to hit
play on those
cool so first of all I'm just super happy that this is working since this is
one of the first times I've tried this and we have a measurement here that we
can look at and coherence is actually pretty good through here
so what information can I take away from this well let me zoom in so I'll go to
my zoom preset one now I'm just looking at like 30 Hertz - what is this 400
and this is hard for me to understand I got to tell you guys because I'm used to
measuring a reference signal like you know peak noise coming out of the
generator here too my measurement signal in the room they should be exactly the
same in some regards but this I'm looking at two different microphones but
the same source signal so what's happening here I think it can help to
review the user's manual here just a couple of lines so this line here if
there is an overall level difference between the two signals the center line
of the measurement moves up or down on the graph
if the reference and measurement signals are identical in level at all
frequencies the magnitude trace is a flat line okay so I obviously don't have
a flat line but I can say in magnitude that where I have a measurement of zero
dB that's where they meet an equal level so what does this say 85 Hertz and 106
Hertz so I wonder if I can go back to my single channel measurements and compare
that let's find 85 Hertz
yeah it looks like they're matching in level there and what did I say 106
yeah and they're matching level there okay so that makes sense to me that's
why we have zero DB here here and I guess up here and it's hard to tell
exactly what's happening in here because of our loco here initially what I'm
thinking is okay in places where we have matching level we probably also want
matching phase now what's going on in the phase here I'm going to rotate this
around a little bit let's go back to the manual as well and see what we can learn
about the phase graph
okay
so phase is a measure of the relative time relationships between two signals
as a function of frequency
the slope of the phase trace is flat when the reference and measurement
signals for the transfer function are identical and arrive at exactly the same
time so what is flat we don't actually see anything perfectly flat here but
Christian zeros from rational acoustics has been helping me look at this and he
was explaining to me that he considers this area in here to be flat so let's
draw a line and say hey this area in here is flat why because it
slopes this way
so that stuff's arriving late and then it slopes this way so that stuff is
arriving early so anything in between there is arriving on time
so even though it doesn't look exactly flat this is what's arriving on time so
now I'm thinking okay how can I match up the stuff that is arriving on time and
the stuff that is also matched in level right now we've got this area arriving
on time
it's and that's not exactly what I need what
I really need is kind of this stuff in this area to arrive on time okay
so let's see if we can make a change here let's go over to logic
open up this delay and let's add one millisecond
oh wait I forgot to save the trace
I'll save this
the way reset the averages
cool so now we can see it's changed a little bit that flat area is no longer
exactly right there we can say that let's cut these
I think we could say that it's moved up here
a little bit right all right so let's keep going because it
seems like we're kind of shifting it over to the left two milliseconds preset
averages
okay so let's just delete this
so now we might say that we are now getting a flat area potentially all the
way through here let's say it at least to here right
let's add one more millisecond and see what that does
I'm going to maybe rotate this around here so see this where this looks kind
of crazy through here
I'm going to kind of ignore that because of this coherence here
okay and now I think that we can say that we've kind of got flat going on at
least to here maybe all the way to here
so as you can tell as I was making those changes nothing was happening up here in
the magnitude trace so this is not summation it's still just relative level
differences so I didn't make any changes to the relative level if I were to come
over here and turn this guy down 10 DB reset averages now we would see a change
in the magnitude trace okay so let's reset that
okay so I've changed we're on time is in the phase graph here between these two
microphones I added some delay and now on time is
over here in this area which is what I was going for since this is where we've
got a closer match and level okay I could also look at moving it down here
or up there but this is what I decided to go for okay how can we tell if this
has made an improvement okay so over here in logic I also sent both of these
signals to a summing bus bus one and that's now coming into input one so
before we look at that let's turn off this delay
we'll go over to back to our spectrum view let's hide everything except for
our some here's the sum I'm going to turn on the averaging really high
and let's just let that settle down
you
I'll save that and I'll call the odelay
now let's come in here and turn the delay back on my three millisecond delay
let's reset the averaging
cool these colors are kind of hard to see let me check
you
okay blue is where we were that was with no delay and now
orange is the changes we've made let me zoom in here make this a little bit easy
to look at
okay so in the area where do we make our changes that we now we're sort of flat
between let's say 63 and 160 so now between 63 and 160 we have more
summation that's how much do we actually gain so here we're at 50 DB and here
we're at 45 so we gained 5 DB of summation through this area where we
made the Flay the phase or flat and maybe them both arrive in time at those
frequencies you can see that we lost some summation in this area and if we
sort of scroll to the right here you can see it's not all games
cool so this is all I've learned so far if you guys do this on your normal set
of procedures I hope in the comments you'll let me know how you do that stuff
I don't know if I'd actually be doing this in the field because it seems to
take a little bit of time I would definitely do it with a recording or if
I was working on a show where like a play would be great if you're on tour
with the play and you're using basically the same setup every night or I guess
even a concert any show that you're doing the same set up every night this
would be great right you could really compare your channels see what time
things are arriving and choose at what frequency ranges you want to get
summation maybe you don't want summation in some frequency ranges you know these
are creative decisions tonal decisions but now I've kind of learned how you can
do this in smart and I hope this is helpful to you guys so if you have any
questions let me know in the comments all right thanks