> David, can you please give us all a description of your the listening
> situation you are in when you judge these two recordings? Headphones,
> loudspeakers, distance between the loudspeakers, size of room e.t.c?
Klas,
My ears were trained to broadcast standard to judge mono and stereo through=
headphones for absolute level and placement. I rarely had to refer to the
meters on my Nagra IV S or SQN mixer on video. I could peak to +8 without
looking.
I test my ears regularly for frequency response (useable up to 12K, residua=
l
to 15K - not bad for 73), and more importantly for stereo image judgment, u=
p
to 9 sonels. (Left, middle, right, half left, half right, and 4 more
intermediate) I double check my conclusions with close speakers in a 1 metr=
e
triangle in an absorptive bedroom and on the lounge hi-fi system, and these=
match well except perhaps the reflective lounge.
For stereo testing, I use real recordings and an impulse sound to check tim=
e
difference stereo. This distinguishes a 6 samples time difference at 48000=
sps giving around 6 degrees sonel spacing on a 60 degree wide speaker angle=
,
but this is not linear for time difference stereo alone. For volume
difference stereo, I also use narrow bandwith filtered white noise bursts.=
There is a more linear distribution using Audacity's pan pot percentages
where 10% correlates quite well with 1 sonel/6 degrees.
The ultimate check is listening outside. I have lost most of the pinna of m=
y
left ear due to surgery and this caused me some loss of stereo imaging, so =
I
made a fuss and the hospital made me a prosthetic ear which restored my
stereo free air image.
There is a fundamental difference between headphones and speakers with
out-of-phase stereo. With speakers, I get a nebulous unfocussed sound from=
out of phase elements such as background noise or birdsong outside of the
stereo sweet area of pickup, but on headphones, I get a rear image from
these.
I define three elements to a stereo recording.
1) Volume level placement.
2) Time difference reinforcement of the volume level stereo. This is not
essential for good stereo. For instance much music uses just pan pot volume=
level stereo placement of sources. However, time difference does make volum=
e
level stereo a bit sweeter and more focussed in the centre.
3) Reverberation. By definition this is out of phase sound content whether=
heard by the ears or recorded. My rule of thumb is that out of phase conten=
t
should not exceed in-phase stereo background sounds. With most stereo rigs=
you get out of phase results from the rear or sides of the rig, particularl=
y
with an M-S array when S is greater than M. This can detract, for instance=
in woodland where you are surrounded by birds and some are unfocussed.
Out of phase stereo with any mic rig can be easily tested by the shaking
peanuts test, walking around the rig. With my crossed gunmic rig, I get all=
sorts of effects from the rear lobes, but these are generally lower level
that the prime front sound.
In the early days of stereo the BBC sent me out to do an interview with a
gunmic/fig-8 rig on a light aircraft airfield. I had prop planes madly
zig-zagging all over my stereo image as the fig-8 went in and out of phase=
with the rear lobes of the S mic. They of course used the M gunmic output o=
n
its own and panned the stereo in dubbing.
David Brinicombe
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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