LOCALIZATION IN LISTENING ROOMS -HOW TO MAKE COINCIDENT RECORDINGS SOUND AS It is usually desirable to make the stereo image spread across the complete span …
SPACIOUSNESS AND LOCALIZATION IN LISTENING ROOMS -HOW TO MAKE COINCIDENT
RECORDINGS SOUND AS SPACIOUS AS SPACED MICROPHONE ARRAYS
David Griesinger
David Griesinger Recordings and Lexicon Inc
Cambridge, MA 02140
ABSTRACT
Examining low frequency localization and spaciousness in typical listening
rooms reveals that low frequency separation is altered by conventional
loudspeakers and positions, with many common placements producing poor
spaciousness when excited by either coincident or pan potted recordings
spaciousness and localization can be enhanced electronically, and when this
is done coincident microphone techniques can produce superior sounding
recordings in a wide variety of playback environments
INTRODUCTION
The investigations which have led to the synthesis in this paper have been
very exciting for me, since as they have proceeded, more and more of the
subjective observations I have accumulated while recording classical music
have become both more objective and more predictive
This is a paper about recording and playback of two
channel stereo Of the
many important aspects of the recording engineers job two are specific to
this medium: Localization, or placement of instruments and voices in the
stereo field, and spaciousness I will assume that spaciousness or spatial
impression sometimes also known as depth, richness, envelopment, or guts
is just as important in recorded sound as it is in concert halls Creating
interesting vocal placements and the illusion of spaciousness are two of
the major duties of the recording engineer
The paper will cover a lot of ground in a very short time As a guide, I
will outline the path of the paper first I will :
Examine the accidental discovery of a recording technique which
simultaneously produced both excellent imaging and spaciousness, and show
how i t relates to the work of Barron, who showed that the impression of
spaciousness is related to lateral sound velocity at low frequencies across
the listeners head
Follow this lead into an examination of how low frequency lateral velocity
in a listening room depends on the recording technique and the speaker-room
interaction; finding that some speaker placements are inherently more
spacious sounding than others, and that
common placements with less
spaciousness can still sound excellent if the recording has enough L-R
information at low frequencies
Examine how localization of sounds in a listening room depends on both
frequency and the placement of the speakers; finding that common speaker
placements tend to reduce separation at low frequencies, effectively making
the image too monaural
Suggest that many of the localization changes caused by rooms can be
corrected electronically, and that spaciousness of coincident or pan potted
recordings can be enhanced in the same way –by increasing the separation
of the stereo signal at low frequencies
End with a discussion of coincident microphone technique, with particular
emphasis on capturing adequate spaciousness Since the localization of
instruments in the sound field and the over-all spaciousness of the sound
is highly dependent on loudspeaker position, discussions of mike technique
between individuals who use different speaker placements are not likely to
be very productive My aim is to bring a little more science into the art
of recording music, and to reduce the degree of misunderstanding in
discussions about it
A
DISCOVERY
This work started with an attempt to explain a fortuitous accident The
first trial recording made with a home-built Soundfield microphone had even
better depth and spaciousness than a simultaneous recording made with an
array of spaced microphones This was the opposite of what I expected In
addition it had accurate imaging and a realistic sense of the original
concert hall Later recordings made of the same group and hall with a
commercial Soundfield microphone had good imaging, but did not have the
same spaciousness or depth
The first clue came from Michael Barrons paper on Spatial Impression SI
Barron showed SI is primarily a low-frequency phenomenon, depending mostly
on the lateral sound energy below 400Hz arriving at the listeners head
between 10 and lOOms after the direct sound This frequency dependence of
SI is a significant addition to the work of Schroeder and Ando on the
importance of minimizing interaural cross correlation for the subjective
attractiveness of sound By manipulating the spatial properties as a
function of frequency the recording engineer has a chance to control
factors in the sound which influence spaciousness, depth, richness,
envelopment, and
guts all of which may mean the same thing without
affecting factors which influence placement
It is the lateral sound energy which creates pressure differences between
the two ears of a front-facing listener at frequencies below 700Hz The
easiest way to measure or think about lateral sound is in terms of the
lateral or Y axis sound velocity, which one can measure with a sideways
facing figure of eight microphone See Fassbender Fassbenders measurement
technique is ideally adapted for use with a Soundfield microphone, which
can be viewed as three figure of eight capsules and one omni capsule in a
single case
Lateral sound velocity obviously determines both localization and
spaciousness, since without it we would hear only mono However it is only
when the lateral velocity and the pressure are in phase or correlated
that localization appears to be possible See Blauert When the velocity
and pressure are uncorrelated or vary rapidly in phase with frequency, a
sense of spaciousness appears to result As will be shown later, lateral
velocity is generated by the L-R or side signal in a stereo recording, even
in a reverberant room, although the room can play havoc with the phase
The
fortuitous accident described above resulted from the equalization of
the side or L-R signal in the mix-down of the trial recording The
frequency response of the prototype microphone was unknown at the time of
the trial recording A1l four patterns were recorded on a four channel
recorder and were equalized and mixed later entirely by ear The
equalization of the three figure of eight signals and the one omni signal
is very important in Soundfield theory, since when done exactly right it
makes the derived patterns independent of frequency when the sound is mixed
to stereo On the trial recording this had been done by ear, with no
interference from either measurement or theory On checking my notes I
found the side facing figure of eight always the L-R signal in a
Soundfield recording had been given a bass boost relative to the omni
output of about 4 dB The omni response ends up being a major component of
the LR signal In this recording a specific departure from frequency
independence of the microphone patterns was desirable
The circuits shown in figure 1 were built to test this observation They
allow the energy in the LR and L-R components of a stereo recording to be
manipulated They
are all simple examples of a class of circuits I will
call spatial equalizers They use single-pole-single-zero shelving filters
Various recordings were tried in the rooms shown in figure 2, and the
spaciousness compared with and without spatial equalization Circuit 1
increased the low-frequency loudness on most recordings, a pleasant side
effect which masked the desired spatial comparisons Circuit 2 appeared to
affect spatiality only, and so it was used for most tests Typical bass
boosts in the L-R signal and cuts in the LR were about 4dB, with the 2dB
point being at 600Hz 300Hz and lkHz were also tried, but the results were
not as pleasant Listening tests were performed with conventional
recordings and with 4 channel B format tapes from the commercial Soundfield
microphone
The judgments summarized below were made subjectively, mostly by the
author, but also by several friends with recording experience Effects of
speaker position were performed by switching between pairs of 4 identical
loudspeakers, a test which is highly revealing of spatial effects Blind
tests were performed by having one person fading in and out circuit 2 while
another tried to guess whether it was in or out
In general the spatial
improvement of circuit 2 was easily heard -if the listener had any
uncertainty or made errors the result was scored as inaudible
SPACIOUSNESS
Listening tests were made for spaciousness as a function of recording
technique and speaker placement
Effects of recording technique on spaciousness:
A Both Soundfield and other coincident recordings were almost always
improved by circuit 2
B Multi-miked recordings where the hall sound was recorded with a spaced
pair or triplet were not improved much by spatial equalization -in fact on
some purist recordings done with only two spaced microphones the effect of
circuit 2 was inaudible
C One commercial classical recording from a major German record company
was improved dramatically by circuit 2, and several multi-miked pop
recordings were also helped
Effects of speaker position on spaciousness:
Effects of speaker position were checked using a recording of Handels
Israel in Egypt made with the commercial Soundfield microphone and no
spatial equalization The effective patterns were hypercardioid at 135
degrees
A When the loudspeakers in rooms 1,2, and 3 were placed so the
woofers
were in the mid-plane between the floor and ceiling in the narrow end of
the room the effect of circuit 2 was almost inaudible on any recording
This position gave less bass energy, frequently poorer localization, and
more spaciousness than other positions
B Speakers on the floor or in the corners of the narrow end gave poorer
localization of low frequency sounds, and increased spaciousness The sound
was muddy
C Speakers in the common 1 to 2 feet off the floor position in the narrow
end gave good low frequency localization, reduced low frequency separation,
and poor spaciousness Music sounded good with this position, but too
monaural in the bass with coincident recordings
D Speakers placed near the floor along the long wall of a small room
appeared to both localize better at low frequencies and give more
spaciousness than speakers placed near the floor in the narrow end
E A test of dipole speaker systems was made with 2 pairs of identical
small speaker systems was arranged in position B of room 1, with the two
speakers in each pair pointing away from each other with a 2×3 plywood
baffle between them They were wired so the backwards facing speakers were
either 1 out of
phase with the front speakers, 2 in phase, or 3 off
This system showed that when the back speakers were out of phase with the
front dipole radiation the sound was always either the same or more
spacious than with a standard direct radiator With dipole radiators
circuit 2 was usually inaudible or unnecessary except for room 2 position
B, where it made an improvement in localization
F Circuit 2 improved the sound of coincident recordings in the free-field
set-up of figure 5, although not as dramatically as it improved the sound
of rooms
On coincident or pan potted recordings where circuit 2 made a significant
improvement, the subjective impression of the recording without
equalization was that it was too flat The bass appeared to be cramped
between the loudspeakers, and in the worst speaker positions actually
appeared to localize inside the listeners head This is not a pleasant
sensation, and did not occur with spaced microphone recordings
LOCALIZATION
Listening tests were made for localization as a function of frequency and
speaker position
The spaciousness experiments and some calculations of the effects of room
modes on localization suggested
that low frequencies should be difficult or
impossible to localize in a room Localization would be determined by high
frequencies, and localization of these frequencies would be reasonably
independent of speaker position A set of localization experiments using
pan pots was devised to test this, and the data showed both hypotheses to
be wrong
In these experiments the subject listened alternately to a single
loudspeaker and to two stereo loudspeakers between which a monaural source
was moved with a pan pot The pan pot was adjusted until the image from the
stereo pair was as close as possible to the position of the single
reference loudspeaker The experiment is similar to one by Dutton, and many
other experimenters have used similar set-ups The difference between this
work and that by Dutton, Ando, Blauert, and others is I am specifically
interested in localization as a function of frequency in average rooms The
experiment was easy to set up, and surprisingly revealing The data have
been plotted in the figures using the numbers printed on the pan pot as a
reference Figure 4 shows the pan pot calibration to be very close to a
cosine law, which is the the directional dependence of the
Blumlein
coincident array figure of eights at 90 degrees
Initial results with 1/3 octave filtered noise as a source showed it was
indeed hard to localize low-frequency sounds Hbwever, after some
experimentation it was found that filtered speech –in this case a monaural
recording of Alistair Cooke filtered with the adjustable band-pass filter
shown in figure 3– gave consistent data and frequently very sharp
localization, even at frequencies below 400Hz The requirement for
localization was speech and adequate bandwidth For low frequencies one to
two octaves of bandwidth seemed to be necessary
The low and high frequency bands were chosen to test separately the two
modes of directional hearing as described by Blauert Below 700Hz the ear
determines direction through phase differences between the ears induced by
diffraction of a plane wave around the head The envelope of the signal is
not detectable Above 15kHz small time differences in the envelope and
pinnae effects are used for localization These two means of localization
were expected to be influenced, by the room in different ways
The results are shown in figures 5 to 9, and discussed below Ideally the
acoustic position of the
source in these graphs should lie on the dotted
diagonal line In general the acoustic positions lie below this line,
indicating the phantom sources seem to be closer to the mid-point between
the loudspeakers than they should be Recordings played through these
systems will appear to have too little separation
It was always possible to tell the position of the reference loudspeaker,
even When the frequency band was 100 to 300Hz The ear is good at
determining the direction of speech in small rooms Thus a test signal
panned full right or full left always appeared to come from the appropriate
loudspeaker The interesting part of the experiment came When signals were
panned somewhere between the two loudspeakers In this case When the pan
pot was in set to center monaural , the acoustic image was almost always
well defined , and localized in the proper position It WBS pan positions
between the center and full right or left that showed wide variation with
frequency and speaker position
Free field:
In the semi free field condition shown in figure 5 both the low frequencies
and the high frequencies formed sharp images, and panned smoothly and
together across the space between the
loudspeakers They had slightly
reduced separation when compared to a cosine law
Rooms at low frequencies:
The results for rooms were quite surprising Speech in the 180-400Hz band
localized in ways which were highly dependent on the room and the speaker-
listener position With some speaker positions the image produced by the
two loudspeakers was very broad –so much so that it was hard for the
listeners to decide on a single pan pot position Even so when many trials
were averaged the listeners best guess for the proper pan pot position
tended to be relatively consistent With some speaker positions the image
was very sharp For speakers which were on the long wall of a room the
localization was sometimes even sharper than the reference speaker, Which
might appear to be vague The speaker positions with poor low frequency
localization usually also sounded spacious with coincident recordings
Positions with sharp localization were usually improved by circuit 2 Bass
frequencies had a very consistent tendency to localize preferentially
toward the center In other words the pan pot had to be rotated further
than one would expect to get the image to move away from the center
The low
frequency sound also sometimes appeared louder when the pan pot was
in the middle for some speaker positions This effect was investigated by
trying to match the sound level between the test loudspeakers and a
reference placed close to the listener The results showed a 2dB increase
in level when the sound was panned to the center These positions
typically the speakers were 1 to 2 feet off the floor in the narrow end of
the room were a subset of the ones previously found to give poor
spaciousness on intensity stereo recordings, and are the ones which benefit
the most from circuit 2 The dipole radiators described earlier gave vague
low frequency localization, but were never louder When the source was
panned to the center
Rooms at high frequencies:
High frequency localization was unpredictable When speech in a band from
15kHz to 2kHz had a sharp image, that image usually followed the general
curve of the free-field localization shown in figure 5 But this was not
always the case For some speaker and listener positions the pan pot
behaved very strangely Figure 9 shows the HF and LF localization for a
single reference position as the moni tor pair was moved from near the
floor to
above the mid-plane of the room The last graph in figure 9, where
the tweeter was only slightly lower than the listeners head, shows a
tendency for the high frequencies to have too much separation –leaving a
hole in the middle on my test recording
These data are consistent with the experiments of Dutton, who found that
better imaging of speech could be obtained if the separation of the signals
was reduced about 4dB at high frequencies
Summary of localization experiments:
A At low frequencies rooms tend to decrease the separation of images,
compared to the same loudspeakers in free field, effectively pulling
acoustic images toward the center of the room The L-R component of the
signal to the loudspeakers is less effective than it should be in producing
localization — it merely broadens the image and gives leaves a vague sense
of spaciousness
B At high frequencies rooms affect separation less than at low
frequencies, but with some placements they tend to increase separation,
smearing the higher formants and consonants of voices outward toward the
loudspeakers Rooms do the opposite of what recording engineers would like
They decrease the LF separation and sometimes increase HF
separation FOr
coincident or pan potted recordings you would like them to increase
separation at LF for spaciousness and reduce it or leave it alone at
HF
SYMMETRY
Notice that in all the experiments shown here there is some degree of
symmetry in the placement of the loudspeakers and the listening position
The loudspeakers are generally equidistant from the side walls, and the
listener stands or si ts somewhere on the center line of the room Two of
the rooms tested were set up as listening rooms by others, and the
symmetrical arrangement had been chosen after careful listening tests
Most listeners appear to arrange their speakers and themselves
symmetrically in a room, possibly to achieve the best image balance With
such placement the two loudspeakers can independently control the pressure
and lateral velocity components of sound at the listeners head A quick
look at the modal patterns for sound propagation in rooms see Morse will
show that if we take y to be the lateral axis, then modes with even Ny will
produce only pressure at the listening position, and modes with odd Ny will
produce lateral velocity but no pressure In addition, if the
loudspeakers
are in-phase only even modes will be excited, and if they are out of phase
only odd modes will be excited
This means that even in a reverberant room at low frequencies the
difference between the pressure at the two ears is determined mainly by the
L-R component of the stereo signal This effect is easy to measure Figure
10 shows the difference between the pressure and velocity signals in room
1, position A when the loudspeakers are driven in phase and out of phase
The furnishings in this room are very non-symmetric, and no particular care
was taken in the set-up Even so the differences in the curves are usually
greater than 10dB Room modes drastically alter the phase relationship
between pressure and velocity compared to the same speaker placement in a
free field, and this interferes with the ability to localize sounds, but
the modes do not alter the average ratio of pressure and velocity
amplitudes very much when the speaker placement is symmetric With adequate
L-R energy the recording engineer has more ability than one might expect to
reduce the amount of interaural correlation at the listening position
RECORDING
What does all this
mean to a recording engineer?
A Loudspeakers and their positions are important to stereo technique: The
choice you make for loudspeakers and loudspeaker positions will influence
your recording technique The high directivity of electrostatic
loudspeakers at high frequencies may improve high frequency imaging, but
their added spaciousness at low frequencies may cause you to choose
microphones and patterns which sound too monaural on direct radiator
speaker systems Direct radiators in the corners or in the mid-plane of the
room may have the same effect
Engineers should probably take the time to investigate the apparent
position of different frequency bands when a mono source is panned between
the loudspeakers Problems at high frequencies may lead to overly monaural
mixes, and smeared images in general
B Spatial equalization of the room may be useful:
If speaker placement cannot correct the problems mentioned above spatial
equalization in the feed to the monitor system may be indicated In fact,
we may be using our two channel room equalizers in the wrong way When we
equalize a room we should separately equalize the LR and the L-R response,
not the L and R response individually The
equalization of the difference
signal should be adjusted so that the localization of high and low
frequencies coincide, preferably following a cosine law Doing this would
allow more precise imaging and more convincing stereo from most systems
C Widely spaced microphones give good spatial impression but poor imaging
: The work presented here tends to uphold the notion advanced by others
that localization in stereo reproduced through two loudspeakers depends
principally on amplitude differences between the two loudspeakers of
signals which are in phase, as in intensity stereo At low frequencies if
there is also a phase difference the ear simply becomes confused, and a
sharp image is not formed between the loudspeakers Phase differences
contribute to the sensation of spatial impression however, and are vital in
the reverberant sound of a recording for this reason
Thus spaced microphone recordings do not image as well at low frequencies
as coincident recordings High frequency localization is less compromised,
depending as it does on amplitude differences between the two channels,
with phase being unimportant spaced microphones do make recordings with
good SI The hall sound is
recorded with essentially random phase,
guaranteeing there will be sufficient uncorrelated L-R information in the
recording to create adequate lateral velocity at the listeners head, even
when the loudspeaker arrangement produces reduced separation
The industry standard method of recording with two spaced ambience
microphones combined with a large number of pan potted accent mikes can
successfully make recordings with both good imaging and adequate SI, even
when played on speaker systems with poor spaciousness This fact, along
with the ease of use and the control over balance this technique gives, may
account for its popularity
D Coincident techniques are better :
It is my belief that coincident or Soundfield microphone techniques can
produce a superior sound, combining excellent imaging at all frequencies
with a more convincing impression of depth and a more realistic sense of
space A key to achieving this depends on having adequate L-R signals at
low frequency This is will help overcome poor separation in the listening
room and create adequate spaciousness Tb my ears the advantages of
coincident main microphones correctly chosen, spatially equalized, and
placed are apparent
even when accent microphones preferably also
coincident arrays must be employed
COINCIDENT TECHNIQUES
Perhaps the most common coincident technique employs two cardioid or
hypercardioid microphones placed close to each other at some angle For the
sake of this discussion I do not wish to consider the effect of the
distance between them, but will assume the capsules occupy roughly the same
spot Tb understand how to record with coincident mikes it is best to
simplify the problem by making some obvious limits It is usually desirable
to make the stereo image spread across the complete span of the
loudspeakers Tb do this, we want the null point of one of the pair of
microphones to correspond to the peak sensitivity of the other Blumlein
technique figure of eights at 90 degrees does this, and also produces a
cosine law for placement as a function of angle –similar to the pan pot
shown in figure 4
In this and other ways, the Blumlein technique appears to be ideal for
coincident recording Unfortunately it is very seldom possible to use it in
practice Blumlein technique requires that the microphone be far enough
back in the hall that all the musicians fit
within a /- 45 degree angle
from the center of the microphone array Almost invariably this causes the
recording to be too reverberant
Other microphone configurations, such as hypercardioid microphones with 120
degree nulls placed at 120 degrees, also have the peak sensitivity of one I
microphone at the null of the other This configuration is equivalent to an
MS array with a forward facing cardioid microphone unfortunately in this
configuration the level of the two channels as a function of the angle of
the source is no longer a cosine -sources in the center are softer than
they should be by 1 to 2 dB This is usually not bad, since sources in the
center are usually closer to the microphone However if the engineer tries
to compensate for this panning error by I reducing the angle between the
microphones, 2 widening the pattern cardioids at 120 degrees, or 3 by
increasing the LR signal the hall sound, the spaciousness, and the spread
will suffer
With a continuously variable mike such as a Soundfield, the engineer tries
to use patterns which obey the rule that the peak sensitivity of one
microphone should lie on the null of the other Problems with center
balance can usually be solved
by changing the positions of the musicians or
the microphone In this case all signals which come from sources located
between the two peaks in response will be in phase, with an out of phase
region on either side In general the distance of the microphone to the
group is chosen for the best ratio of direct to reverberant sound, and the
angles and the patterns of the microphones are set to include the whole
group in the in-phase region
Now what happens to the hall sound? If we assume we have only patterns
which obey the above rule and that the hall sound is equal in all
directions, only the Blumlein pattern will give equal energy in the L-R and
LR signals This is in part because crossed figure of eights are not sensi
tive to sound in the vertical direction All other patterns which obey the
angle and pattern rule above are produced by adding more and more omni
sound into LR signal, and as a result more and more vertical reverberant
information is added to the total pick-up, making the reverberation too
monaural
This is why many engineers have found that as they move a coincident pair
close enough to a group to get adequate clarity, either the center of the
group is too soft, or the
hall becomes too monaural As they get closer
they must use greater angles between the microphones and wider patterns to
preserve good spread and imaging Even if the pattern/angle rule is obeyed
, the center of the image will get softer, and the hall will be
inadequately spacious Attempts to correct either problem by changing the
patterns or angles of the microphones will make the other worse
If the hall happens to have very little reverberant energy in the vertical
direction this effect may not occur In addition, engineers who work only
with earphones, dipole loudspeakers, woofers in the mid plane between floor
and ceiling, or in overly reverberant monitoring rooms may find no
problem wi th the hall I suspect this is why techniques such as ORTF work
very well for some people Most of us, however, would love to be able to
increase the spaciousness of a coincident recording without affecting the
imaging This is just what spatial equalization does spatial equalization
is usually inaudible when the playback environment does not require it, so
there is no reason not to add it
By applying a bass boost to the L-R signal, and/or a bass cut to the LR
signal the spatial impression of the
hall can be emphasized without
affecting the imaging at higher frequencies Localization of low
frequencies may also be improved This effect may be created acoustically
by choosing microphones which have an inherent rise in the figure of eight
response as the frequency goes down A cardioid microphone is really an
acoustic combination of an omni and a figure of eight If the figure of
eight response rises at low frequencies, the mike may be more successful in
a coincident array If the omni response rolls off the microphone will
still be flat on axis If such a microphone is not available the
equalization can also be done electronically with a circuit such as circuit
2, or with simpler circuits in an MS or Soundfield recording set-up
One final observation on coincident technique:
Spatial equalization results in more energy in the L-R component of a
stereo signal, especially at low frequencies To my ears, it is also
highly desirable in most recordings made with intensity stereo techniques
Ideally perhaps the correction should be applied by listeners, to match
their speakers and rooms However such an arrangement would be unnecessary
on the majority of commercially available
spaced-microphone recordings, and
listeners are unlikely to feel obliged to do it If the engineer simply
applies the needed correction to the master tape the record cutting
engineer may be unhappy He or she neednt cry too hard; most coincident
recordings have more in-phase energy than recordings made with spaced
mikes, and engineers have been cutting spaced mike recordings for years
Although the peak vertical component of a coincident recording made with
spatial equalization may be no greater than an equivalent spaced microphone
recording there is one important difference
Phase meters have become popular lately, especially in Germany A spaced
microphone recording tends to have essentially random phase, which simply
reads zero on a phase meter Engineers have grown accustomed to this, even
though the peak vertical amplitude may be large A coincident recording
with spatial equalization tends to have high correlation between the two
channels
When the vertical component is large, the phase meter will probably read
negative for a moment Until engineers become familiar with this, and
realize the effect is benign, there may be some adverse reaction In any
case mono compatibility is much
better in a coincident recording with
spatial equalization than in any spaced recording Perhaps the ascendancy
of the compact disk will finally lay to rest the obsession with monaural
bass which is so common among recording engineers
CONCLUSIONS
There are three major conclusions from this work:
A Loudspeakers and their positions are important to stereo technique, with
many common positions giving less spatial impression, good localization,
and reduced separation at low frequencies In addition some positions give
higher spatiality and poorer localization than the same speaker geometry in
a free field Spatial equalization of the room may be useful to make
localization and spaciousness closer to that of the same loudspeakers in a
free-field
B Recordings made with widely spaced microphones give good spatial
impression but poor imaging -if fact it is in part the ability of these
recordings to sound spacious in any playback environment which accounts for
their popularity
C Coincident techniques with spatial equalization can produce superior
imaging, excellent spaciousness, and a realistic impression of the original
acoustic space
Readers who have
lasted this far are encouraged to try a spatial equalizer
such as circuit 2 on a number of recordings, especially ones which sound a
little flat If you can hear no difference on a coincident recording you
are probably using a speaker position with high inherent spaciousness and
poor low frequency imaging If this is true and you are also a recording
engineer, be advised that not all the customers of your products are
listening the same way you do Recording engineers who have tried
coincident techniques in the past without success are urged to try again
ACKNOWLEDGEMENTS
I would like to thank many people for their help in doing these experiments
and preparing this manuscript, especially Harriet Griesinger, Brad Meyer,
Rene Jaeger, and Frank Cunningham Kristen Beard, Will Eggleston, and Chip
Powell also contributed to the listening tests Charles Bagnaschi at
Lexicon was very kind to lend equipment and space to do this research
REFERENCES
Ando, Y and Imamura, M Subjective Preference Tests for Sound Fields in
Concert Halls Simulated by the Aid of a Computer J Sound and Vibration
652, pp 229,239 1979
Ando, Y Subjective
optimal Conditions of sound Fields for Recording and
Reproducing presented at the 96th Meeting of the Acoustical Soc of am,
Honolulu, Hawaii, 1978
Barron, M and Marshall, AH Spatial Impression due to Early Lateral
Reflections in Concert Halls: The Derivation of a Physical Measure J
Sound and Vibration 772 211,232 1981
Blauert, J Spatial Hearing MIT Press, 1983 -This work was originally
published in German under the title Raumliches Horen by S Hirzel Verlag,
Stuttgart
Cooke, Alistair Talk About America BBC record PYE 2-701 AlV Records Inc
3 W57th St New York, NY 10019
Dutton, G The Assesment of two-channel Stereophonic Reproduction in
Studio Monitor Rooms, Living Rooms, and Small Theaters J Audio Eng Soc
10 2 1962 pp 98,105
Fassbender, J Uber Messungen des Seitenschallanteils in Verschiedenen
Salen und in Raummodellen Applied Acoustics 16 1983 pp 11-30
Lipshitz, SP Stereo Microphone Techniques: Are the Purists Wrong?
Presented at the Audio Eng Soc Convention in Anaheim, May 1985 AES
preprint 2261
Morse, PM Vibration and Sound McGraw Hill, 1948 pp 389,390
Plenge, G Uberlegungen zur Stabilitat und Leistungsfahigkeit
verschiedener stereofoner Ubertragungsverfahren presented at
the 13th
Tonmeistertagung , Munchen 1984
MR Schroeder Comparative Study of European Concert Halls and Correlation
of Subjective Preference with Geometric and Acoustic Parameters J
Acoustical Soc of JIm 16 G32 1965
Smith, J H Ambisonics-The Calrec Soundfield Microphone Studio Sound
Ck:t 79 pp 42-44
Source:in.gov
