Log in

View Full Version : Delay between room and spot mics


Tim Sprout
April 23rd 14, 05:32 PM
How do you fix the delay between a room stereo pair and spot mics? Do
you record a spiky sound like a cowbell hit and visually align the peak?
Measure the distance between the mics with a tape measure and calculate
it? Slide the tracks and adjust by ear? At what distance does this
become a problem?

Thanks much,

Tim Sprout

Mike Rivers[_2_]
April 23rd 14, 05:42 PM
On 4/23/2014 12:32 PM, Tim Sprout wrote:
> How do you fix the delay between a room stereo pair and spot mics? Do
> you record a spiky sound like a cowbell hit and visually align the peak?
> Measure the distance between the mics with a tape measure and calculate
> it? Slide the tracks and adjust by ear?

Any of the above will work. Recording a spike that reaches all the mics
is probably the most accurate method.

> At what distance does this become a problem?

The critical comb filtering region, where combining mics at close to the
same level will cause raggedness in the frequency response, is roughly
0.5 to 5 milliseconds, which roughly corresponds to about 1/2 to 5 feet
difference between the source and each mic. It takes about 30
milliseconds (30 feet) before you can perceive the difference as an
echo. In between, your ear is the best guide.


--
For a good time, visit http://mikeriversaudio.wordpress.com

Frank Stearns
April 23rd 14, 09:12 PM
Mike Rivers > writes:

>On 4/23/2014 12:32 PM, Tim Sprout wrote:
>> How do you fix the delay between a room stereo pair and spot mics? Do
>> you record a spiky sound like a cowbell hit and visually align the peak?
>> Measure the distance between the mics with a tape measure and calculate
>> it? Slide the tracks and adjust by ear?

>Any of the above will work. Recording a spike that reaches all the mics
>is probably the most accurate method.

Dog trainer clicker available for $1.50 at most pet stores works great. Just make
sure you originate your clicks at the right place (where the instrument will be).

>> At what distance does this become a problem?

>The critical comb filtering region, where combining mics at close to the
>same level will cause raggedness in the frequency response, is roughly
>0.5 to 5 milliseconds, which roughly corresponds to about 1/2 to 5 feet
>difference between the source and each mic. It takes about 30
>milliseconds (30 feet) before you can perceive the difference as an
>echo. In between, your ear is the best guide.

Indeed. And this might be the only way to make the adjustment if there are multiple
varied paths involved -- there will be no "correct" solution. So, do it by ear; use
the spot as little as possible and still get the sound you want. Sometimes you'll
only have a 3-5 sample window where things sound sweetest. A delay with sample
resolution and that you can single-sample step is useful.

Also beware of musicians who move around a lot. This might mean you have to
dynamically change your delay in post, depending on the geometry of the stage layout
and microphone heights.

Frank
Mobile Audio
--

Scott Dorsey
April 23rd 14, 09:16 PM
Tim Sprout > wrote:
>How do you fix the delay between a room stereo pair and spot mics? Do
>you record a spiky sound like a cowbell hit and visually align the peak?
>Measure the distance between the mics with a tape measure and calculate
>it? Slide the tracks and adjust by ear? At what distance does this
>become a problem?

Slide the tracks and adjust by ear. You will hear it when it pops into
place.

In general about 1ms/ft.

It will be more obvious with the spot mike up very loud... get it right,
then drop the level back down to normal.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Tom McCreadie
April 24th 14, 12:58 PM
Scott Dorsey wrote:
>
>Slide the tracks and adjust by ear. You will hear it when it pops into
>place.

When sliding tracks, I find it easier to home in on the registration point if I
mono the mains and route it to one headphone channel, while the similar level
spot is routed to the other ear. Adjustment is akin to manually focusing a
camera: you typically have to first go beyond the synch point and ease back
again. I'd then confirm with the cans reversed on my head.

But of course precise time registration of the spot may not give the optimum
audio result.
--
Tom McCreadie

Sudden Death Syndrome? Sounds serious - what are the symptoms?"

Dave Plowman (News)
April 24th 14, 01:52 PM
In article >,
Tom McCreadie > wrote:
> Scott Dorsey wrote:
> >
> >Slide the tracks and adjust by ear. You will hear it when it pops into
> >place.

> When sliding tracks, I find it easier to home in on the registration
> point if I mono the mains and route it to one headphone channel, while
> the similar level spot is routed to the other ear. Adjustment is akin to
> manually focusing a camera: you typically have to first go beyond the
> synch point and ease back again. I'd then confirm with the cans reversed
> on my head.

> But of course precise time registration of the spot may not give the
> optimum audio result.


Makes you wonder how anything sounded decent in analogue days. ;-)

--
*Work like you don't need the money. Love like you've never been hurt.

Dave Plowman London SW
To e-mail, change noise into sound.

Frank Stearns
April 24th 14, 03:08 PM
"Dave Plowman (News)" > writes:

>In article >,
> Tom McCreadie > wrote:
>> Scott Dorsey wrote:
>> >
>> >Slide the tracks and adjust by ear. You will hear it when it pops into
>> >place.

>> When sliding tracks, I find it easier to home in on the registration
>> point if I mono the mains and route it to one headphone channel, while
>> the similar level spot is routed to the other ear. Adjustment is akin to
>> manually focusing a camera: you typically have to first go beyond the
>> synch point and ease back again. I'd then confirm with the cans reversed
>> on my head.

>> But of course precise time registration of the spot may not give the
>> optimum audio result.


>Makes you wonder how anything sounded decent in analogue days. ;-)

Well, often they didn't. Badly done multi-microphones on orchestra and chorus was
fairly awful, but it was "accepted." When we were finally able to do it right and
use aligned spots only as clearly needed rather than just because they were
there, it was a whole new improvement in the art.

Frank
Mobile Audio
--

Scott Dorsey
April 24th 14, 06:39 PM
Dave Plowman (News) > wrote:
>In article >,
> Tom McCreadie > wrote:
>> Scott Dorsey wrote:
>> >
>> >Slide the tracks and adjust by ear. You will hear it when it pops into
>> >place.
>
>> When sliding tracks, I find it easier to home in on the registration
>> point if I mono the mains and route it to one headphone channel, while
>> the similar level spot is routed to the other ear. Adjustment is akin to
>> manually focusing a camera: you typically have to first go beyond the
>> synch point and ease back again. I'd then confirm with the cans reversed
>> on my head.
>
>> But of course precise time registration of the spot may not give the
>> optimum audio result.
>
>
>Makes you wonder how anything sounded decent in analogue days. ;-)

1. Folks avoided spot-miking when they had mixes based around a main pair
(which is still a good idea) or they avoided using a main pair for mixes
based around spots (which is sometimes a good idea but usually not in my
opinion).

2. Folks specifically positioned the main pair far enough back from the stage
that the delay to the main pair was exactly the delay between the record
and play heads on the tape machine and then they used sel-sync to line
them up. This worked really well on an ATR-104 but worked very poorly on
older machines whose audio quality in sync was poor.

3. Rock bands made "live albums" that were, in fact, almost completely
retracked in isolated studios.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

William Sommerwerck
April 24th 14, 08:35 PM
"Dave Plowman (News)" wrote in message ...

> Makes you wonder how anything sounded decent
> in analogue days. ;-)

Who said it did?

Luxey
April 25th 14, 01:08 AM
I'm not sure any method really works, except by ear in some idealy controled environment. Align all spot mics to main paair, and have them all remain unaligned with each other. In small rooms, with loud bands where each mic is picking everything...