Recording Brass & Reeds
RECORDING BRASS & REEDS
Brass and reed instruments present some challenging problems to the recording
engineer, whether played by soloists or sections. Hugh Robjohns offers some
hints and tips.
Recording any musical instrument is a challenge if you want to capture a faithful rendition of
the performance without distorting the tonal quality of the instrument or veiling it with
undesirable mechanical noises. It seems to me that every instrument -- and I include the
human voice in that description -- presents its own unique set of problems and solutions,
and in this article I shall be looking at some of the techniques and pitfalls of recording brass
and reed instruments, both as played by soloists and in sections.
As with any musical instrument, placing the microphone is much easier if you have an
understanding of how the instrument works -- where the sound comes from, how it radiates
from the instrument, and what its frequency and dynamic range is. So let's start with a brief
look at the most common brass instruments to get a feel of what is involved.
The Brass Instruments
The full family of brass instruments as we know them today, including
the cornet, trumpet, trombone, tuba, and euphonium, date from about
1850, by which time their designs had been optimised. The last major
evolution was the invention of the valve as a means of introducing or
bypassing sections of tubing and thereby allowing the performer to
alter the tuning of an instrument whilst playing. Previously the only
http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Página 1 de 7
27/06/2001
Página 2 de 7 Recording Brass & Reeds
means available was a slide (like the modern slide trombone), and
although short-slide trumpets were popular in the 19th century, the valve offered a more
practical solution.
The basic principle of the trumpet (and its cousins) is that blowing into the tube through taut
lips sets up an audibly resonant vibrating column of air. Changing the tension of the lips
and the air pressure allows different harmonic resonances to be stimulated, thus providing
a limited number of alternative notes, with big gaps in the lower register and not all the
available harmonics conforming to the diatonic scale. However, altering the fundamental
length of the pipe (with valves or a slide) enables a full and accurate compass of notes to
be generated. The tonal qualities of the instrument are determined by the metal alloys used
in its construction, the shape of the bell and the bore size of the tubing -- the latter
determining the balance of harmonics and the instrument's volume capabilities amongst
other things.
A characteristic of brass instruments which everyone knows is that they are all very loud!
However, their loudness varies with pitch, because it requires much more energy to force
the tube to resonate at the higher harmonics. For example, measured at four metres, a
trumpet can produce well in excess of 96dB SPL, and easily over 130dB within 0.5m of the
bell! At low registers the quietest notes possible (without using aids like mutes) would be
around 60dB SPL (at 4m) but high notes will not be less than around 86dB SPL -- the
trumpet has about twice as much dynamic range at the bottom of its range than at the top.
By comparison, a trombone is not only capable of around 5dB greater volume than a
trumpet, but also has a wider dynamic range.
In terms of the frequency spectrum, brass instruments all tend to be rich in harmonics. For
example, although the fundamental of a trumpet is centred around 1200Hz, it generates
strong harmonic components beyond 8kHz for the upper notes, with the implication that the
harmonic series continues well into the ultrasonic region. The harmonic balance also varies
enormously with volume, the fundamental and first overtone remaining relatively constant
but the upper partials exhibiting a much greater dynamic range. Thus the trumpet (see
Figure 1 below) can sound quite mellow when played softly, but brilliant when blown hard.
The trombone, on the other hand, has its fundamental centred around 550Hz (see Figure
2), but can produce frequency components above 10kHz when played hard. When played
more softly, however, the balance of harmonics doesn't change quite as much compared to
the trumpet, so it retains much of its rich and bright quality even during quieter passages.
The lowest brass instruments are the bass and contrabass tubas (and their relatives) which
are capable of generating notes as low as 29 Hz (a low Bb), although the first overtones are
generally much stronger than the fundamentals.
Reed Instruments
Reed instruments include the clarinet, saxophone, oboe and bassoon amongst others, but I
will concentrate mainly on the clarinet and sax as these are the most common in popular
music. However, the principles discussed here apply broadly to the whole family.
Like the brass instruments, the clarinet matured dramatically in the late 1800s, acquiring
the complex mechanism of keys we know today -- modern clarinets are also a little brighter
and louder than those of Mozart's period (because the reeds used tend to be larger and
softer).
Blowing across the reed forces it to vibrate, and thus stimulate a column of air within the
tube of the instrument to vibrate in sympathy. The effective length of the tube is determined
27/06/2001 http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Página 3 de 7 Recording Brass & Reeds
by the keys which reveal holes setting the acoustic length of the resonant pipe. The key
mechanism is merely a practical method of allowing human fingers to cover and control the
numerous widely spaced holes.
The clarinet produces a sound in which the odd-numbered harmonics tend to predominate
over the even-numbered ones, although in the very highest registers the even harmonics
become stronger. The prevalence of odd harmonics creates the
characteristic 'hollow' sound quality, and these extend well beyond
12kHz for the higher notes. The clarinet probably has the widest
dynamic range of any wind instrument, with the quietest notes
producing around 35dB SPL (close to room ambience) and the
loudest about 90dB SPL (at 2m). However, like all wind instruments,
the dynamic range reduces in the higher registers because there is a
minimum level below which it is not possible to 'blow' a note.
The saxophone is, by any standards, an odd instrument combining a
conical brass tube vaguely similar to that of a trumpet, with a reed
mouthpiece like a clarinet's! It was designed for use in military bands
by a very influential German instrument maker called Adolphe Sax
who patented his Saxophone in 1846. The instrument's late arrival on the musical scene
has precluded it from anything more than a rare appearance in the classical orchestra,
although it is a mainstay of big bands, military (concert) bands, and of course jazz and pop
music. Not surprisingly, it shares acoustic characteristics with both the brass and reed
family, although it is closer to the clarinet than anything else.
Capable of a very wide dynamic range and possessing a rich combination of harmonics
which extend well up to the 12kHz region and higher, the saxophone is, to all intents and
purposes, a metal-bodied clarinet. However, the increased size of the pipe bore makes it
capable of greater volume, and the bell means that it radiates sound differently.
Recording Brass Soloists
Figures 1 and 2 (on page 189) show how different bands of frequencies radiate from
trumpets and trombones. The high frequency harmonics tend to beam directly to the front
of the bell, with the lower frequencies being radiated over a wider arc. Although it might
seem the most obvious place to position a microphone, the most common mistake is to
position microphones directly on-axis and far too close to the bell.
In a live PA situation, this may be the only possible solution to achieving enough isolation,
but it certainly isn't the best technique for recording! Like most musical instruments, the
sound generated by trumpets and trombones needs space for all the different harmonics to
become properly balanced, and so the microphone needs to be positioned at a respectable
distance from the instrument -- anything from, say, one to four metres depending on the
acoustics of the recording environment.
I would recommend starting with a mic placed at about two metres from the bell and about
30 degrees off-axis. With trumpets it is usually easier to mic from above because most
players angle the instrument downwards, but with trombones I would generally come in
from below. As always, though, placement should be determined by the need to aim the
dead side of the (directional) mic towards the sound sources you wish to reject. Moving the
mic closer will tend to give a cleaner, tighter and brighter sound, whilst moving away will
give a fuller and often more dramatic sound (dependent on the recording acoustics).
Another technique which can be
27/06/2001 http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Recording Brass & Reeds
effective is to have the musician
facing a wall or window whilst
playing. A pressure zone mic taped
to this surface at a suitable height to
be out of the direct firing line does a
remarkably good job of capturing a
clean, detailed sound. This method
also provides a lot of acoustic
feedback for the musician, which
can be an advantage.
Miking too close to the instrument
distorts the tonal balance,
exaggerating some elements and
understating others. This produces
what can only be described as a
'nasty' and unrepresentative noise
which is very hard (if not
impossible) to sort out with EQ.
Similarly, placing the mic exactly
on-axis to the bell not only exposes
it to extreme SPLs and potential
wind blasting, but also
overemphasises the very directional
upper harmonics. Although this
gives a very bright hard sound, it
will tend to vary a great deal in both
level and quality if the musician
moves the instrument while playing
-- and they all do!
Sound levels increase dramatically
with increasing proximity to the
source, and a lot of microphones
simply cannot cope with the sound
pressure level if placed any closer
than a metre or so. Most dynamic
mics would survive and might even
give an acceptable sound, as would
any decent studio capacitor mic
(provided it had a built-in attenuator
to avoid overloading the internal
preamp). However, electrets and
ribbons would not fare so well
because electrets don't generally
have facilities for attenuators ahead
of the preamp (which would almost
certainly become overloaded). I
have even known ribbon mics to
suffer split diaphragms when placed
too close to the firing line of
trumpets and trombones! Having
said that, a ribbon placed on-axis
but at a safe distance can give a
http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Página 4 de 7
Effects And Processing
I mentioned earlier how high notes tend to be louder than
low notes on most brass instruments so, although the
musicians should be able to balance their dynamics pretty
well, it is not uncommon to have to use some compression
to level things out a bit. Brass instruments and saxophones
can also produce very peaky signals which benefit from
some mild compression -- but avoid limiting as this makes
the sound harsher.
The best results are usually achieved by compressing the
recorded tracks during mixdown rather than compressing
to tape (or hard drive) simply because you then know what
you are dealing with and can optimise the threshold and
time-constant settings. Generally, you will require pretty
fast attack and release times, but listen very carefully as it
is easy to destroy the attack and bite of brass instruments.
In the case of saxophones and woodwind, excessive
compression will also emphasise their mechanical noises.
The big, fat brass sounds common on a lot of American
records typically employ a lot of compression, but this is
only possible if the recording is very clean in the first place.
Compressing a poor recording only makes it sound worse
by emphasising spill, poor acoustics and mechanical
noises, so take the trouble to get the best sound possible
in the original recording.
Gating acoustic instruments (other than for effect) is rarely
successful and usually damages the sound unacceptably
before any worthwhile improvement in separation has been
obtained. So I would suggest that if you are having
problems with a lack of separation or with mechanical
noises, the microphones should be repositioned or the
musicians asked to improve their technique! Gating might
reduce the spill between brass stabs, but will almost
certainly remove the all-important attack as well. However,
if you really do want to use a gate, make sure you insert it
before any compression, or it will be impossible to set the
threshold accurately.
If the right microphones have been positioned carefully,
equalisation is rarely needed, although I have found that a
little gentle tweaking at the extreme top can sometimes be
useful. Digital recorders can suffer with brass instruments,
as the high energy at high frequencies can cause aliasing
artefacts which add an unpleasant edge to the sound (this
is common on early machines with dubious filter stages).
Other than using better A-D converters, the only solution is
to record at lower levels, giving the filters a better chance
to reduce troublesome ultrasonic frequencies.
These high harmonics can also affect comparisons
between the sound directly from the console with that after
A-D and D-A conversion from, say, a DAT, as they will be
absent in the latter (assuming 44.1 or 48kHz sampling).
Although subtle, this sometimes comes across as a lack in
'air' or brightness, but resist the temptation to boost the
extreme HF as this will only increase the likelihood of
aliasing distortion.
27/06/2001
Recording Brass & Reeds
very smooth and natural sound
indeed -- but it requires care!
In general, large-diaphragm mics
work best, especially for
instruments playing in the lower
registers, but be careful about
which microphones you select.
Those designed primarily for vocals
tend to have a presence lift in the 2-
6kHz region to improve clarity, but
this usually works against brass
recordings, as it over-emphasises
the upper harmonics lending an
unpleasant 'piercing' quality.
The larger valved instruments such
as tubas, euphoniums and the like
can be mechanically noisy,
although this is mainly down to
playing technique. Since these
instruments all fire upwards, good
results can be obtained by miking
from above and behind so that the player's body shields the mechanical noises from the
mic.
The key to recording reed instruments is to be aware that most of the sound doesn't radiate
from the bell, but from the body of the instrument. In the case of the clarinet and similar
instruments the higher frequencies beam from the bell and rely on being reflected back
from the floor to become properly balanced with the lower harmonics (see Figure 3 above).
This means that to record both the direct and reflected sound, the best mic position is
somewhere between one and two metres away, approximately level with the top half of the
instrument and aiming at the holes towards the lower half of the body from the front. There
is no point in miking near the bell as this will only capture a very weak, thin and nasty
sound!
A common problem is excessive mechanical noise from the keys, but this is largely down to
the skill of the player and there is very little that can be done with microphone position. One
technique worth trying, though, is aiming the microphone from the side instead of the front -
- experiment with both sides to see which is best, and then reorganise the studio layout to
obtain the best spill-rejection from other instruments. The drawback with this technique is
that the overall level and brilliance of the instrument will tend to drop off in comparison to a
frontal position.
Again, the flatter the response of the microphone, the more natural and accurate the sound
obtained. Mics with a peaky presence region are best avoided, as they will tend to
emphasis the squawkiness of the instrument, which is hard to tame with equalisation. Most
professionals favour large-diaphragm mics again -- typically AKG C414s or Neumann
U87s. Small-capsule mics can sound too shrill if not positioned carefully.
The saxophone requires a slight variation in technique because the bell is curved upwards
to project sound forwards instead of towards the floor. Miking the bell directly is a very
Página 5 de 7
Usually, the only processing needed for brass instruments
and sections is the addition of a little reverb. The trick here
is to keep it short (small room settings usually work best)
and avoid adding too much or you will lose the attack and
clarity. Try adding reverb until it becomes obvious, then
pull the fader back between 5 and 10dB!
With bigger brass sections, sometimes the saxophones
(and clarinets if included) have trouble competing with the
trumpets and trombones. Hopefully this kind of difficulty
would have been solved by altering the numbers of
instruments playing at the same time, but if the adopted
solution was to move the mics in closer to the weaker
instruments there will almost certainly be a problem with
the recorded perspective. Typically, when the saxophones
and clarinets are balanced at the right level with the rest of
the band they will sound too close and stand out too much.
Pulling their level back won't cure the problem, just
submerge the woodwind in the mix and the only hope is to
compensate for the lack of perspective with a suitable
early-reflection reverb program and around 10mS of predelay.
Take the trouble to match the reverb as closely as
possible with the studio's acoustic to replace the missing
perspective, and adjust the delay to make the woodwind
sections appear less prominent (taking advantage of the
old proximity effect!).
http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Recording Reeds
27/06/2001
Página 6 de 7 Recording Brass & Reeds
common technique but definitely not the best! As
might be expected, the bell projects only the high-frequency components of the instrument,
and so a very hard, bright, and characterless sound is obtained. However, the technique
does provide good isolation from spill as the mic requires very little gain -- hence the
popularity of the technique for PA purposes.
In the recording studio, a much better technique is to adopt a similar approach to that
appropriate to the clarinet, with a mic aimed towards the middle of the instrument, towards
the player's left hand. Position the mic between a half and one metre away, above and in
front of the instrument, to capture direct sound from the body of the sax combined with the
high harmonics from the bell. Adjusting the angle and distance of a cardioid microphone
relative to the instrument allows the harmonic balance to be optimised.
Sax players are prone to wild movements as they 'get into the groove' and this can present
huge problems for the recording engineer. With greater distance between mic and
instrument, level and quality variations are minimised, but this is not always practical. I have
found rigging a second close microphone three inches from the bell, and telling the player
to keep the instrument immediately below the mic, is effective in helping to keep the
saxophone relatively static!
Recording A Brass Section
A brass section is exactly that -- a composite of (usually) four or more instruments, and I
will assume that it's occupying its standard role in supporting a conventional
rock/pop/blues/soul line-up.
Since a brass section can be a mighty loud thing, recording it at the same time as the
weaker instruments in a band can present serious problems. In a large studio, it might be
possible to put the brass section in a separate booth, or gain sufficient isolation by the use
of acoustic screens positioned in the studio for physical separation from the weaker
instruments. However, separate overdub passes just for the brass can work very well and
this is often the only solution in a small studio. The only drawback with this approach is in
getting the section to play well to foldback, but that is usually quickly overcome with a
couple of rehearsals.
The most common folly is to try multi-miking a brass section with one microphone per
instrument. The multi-mic technique is supposed to allow control of the level of individual
instruments from the sound desk, and demands very good acoustic separation between the
instruments. This isolation is achieved with distance -- maximum distance between different
sound sources, and minimum distance between each microphone and its source. However,
in the case of most acoustic instruments, and especially with brass, very close miking
produces a poor and unbalanced sound. Also, if the musicians are physically close to each
other (as they usually prefer to be) there will be so much spill between the mics that the
whole exercise becomes completely pointless -- all the faders will have pretty much the
same noises on them with no independent control at all, and there will almost certainly be
undesirable phasing effects between the mics!
"Although it might
seem the most
obvious place to
position a microphone,
In my experience the best section sound is achieved
with relatively distant miking, say, a couple of meters,
either with a single mic aimed to provide even
coverage of all players, or with some form of stereo
pair. In the latter case, the precise mic placement will
depend on the size of the section and the kind of
stereo spread required, but would typically be three
27/06/2001 http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
Recording Brass & Reeds
metres in front and a metre or so above the
instruments. It is worth experimenting with bringing the
saxophones in a touch closer to the mic, and pushing
the trumpets and trombones back a little. I'm only
talking a foot or so, but it can make a big difference to
the internal balance of the section.
Página 7 de 7
the most common
mistake when
recording brass is to
position microphones
directly on-axis and far
too closeto the bell."
If only a few musicians are available, but you want
them to sound like the Tower of Power, a couple of
overdubs of additional parts can be a very effective
technique -- especially if the musicians are relocated with respect to the stereo mic to
increase the density of the stereo image. Compressing the final stereo track will also help to
make the section appear more powerful, but beware of over-compressing as this will
emphasise mechanical noises and any spill (including foldback leakage from the
headphones).
With large brass sections, such as in a Big Band, the key to success is in the layout of the
players. Try to have the cornets and trumpets facing the trombones across the studio so
that their spill is on the back of each others' mics, and don't have any other musicians
sitting in front of either section if it can be avoided. This is especially true for the trombones
as they are extremely loud, and not only would it be an unpleasant experience, but it would
be virtually impossible to get a clean sound from any other instrument against the trombone
spill. Position mics at least two metres away from the instruments and aim to use one mic
to cover every four musicians in the brass sections, with one between two in the
woodwinds.
If you find you are having trouble getting the different sections to balance properly, try
listening to the band again in the studio. If the problem exists there too, ask the musical
director to have one or two players in the loudest sections sit out -- it is far more effective
than having to add extra mics or move existing mics closer!
Europe's No1 Hi-Tech Music Recording Magazine
Sound On Sound
Media House, Trafalgar Way, Bar Hill, Cambridge CB3 8SQ, UK.
Telephone: +44 (0)1954 789888 Fax: +44 (0)1954 789895
Email: info@sospubs.co.uk Website: www.sospubs.co.uk
© 1998 Sound On Sound Limited. The contents of this article are subject to worldwide copyright protection
and reproduction in whole or part, whether mechanical or electronic, is expressly forbidden without the prior
written consent of the Publishers. Great care has been taken to ensure accuracy in the preparation of this
article but neither Sound On Sound Limited nor the Editor can be held responsible for its contents. The
views expressed are those of the contributors and not necessarily those of the Publishers or Editor.
27/06/2001 http://www.sospubs.co.uk/sos/jan99/articles/brass778.htm
|
讓我們程式搜尋結果更加完美 如果您覺得該文件有幫助到您,煩請按下我如果您覺得該文件是一個一無是處的文件,也煩請按下我 |
|
該文件您看起來是亂碼嗎?您可以切換編碼方式試試看!ISO-8859-1 | latin1 | euc-kr | euc-jp | CP936 | CP950 | UTF-8 | GB2312 | BIG5 |
|