Outdoor And Indoor Recording For Motion Picture. A Comparative

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Audio Engineering Society Convention Paper Presented at the 122nd Convention 2007 May 5–8 Vienna, Austria The papers at this Convention have been selected on the basis of a submitted abstract and extended precis that have been peer reviewed by at least two qualified anonymous reviewers. This convention paper has been reproduced from the author's advance manuscript, without editing, corrections, or consideration by the Review Board. The AES takes no responsibility for the contents. Additional papers may be obtained by sending request and remittance to Audio Engineering Society, 60 East 42nd Street, New York, New York 10165-2520, USA; also see www.aes.org. All rights reserved. Reproduction of this paper, or any portion thereof, is not permitted without direct permission from the Journal of the Audio Engineering Society. Outdoor and Indoor Recording for Motion Picture. A comparative approach on microphone techniques. Christos A. Goussios1, Christos V. Sevastiadis2, and George M. Kalliris3 1 2 3 Aristotle University of Thessaloniki, Department of Film Studies, Thessaloniki, 54124, Greece [email protected] Aristotle University of Thessaloniki, Department of Electrical and Computer Engineering, Thessaloniki, 54124, Greece [email protected] Aristotle University of Thessaloniki, Department of Journalism and Mass Communication, Thessaloniki, 54124, Greece [email protected] ABSTRACT Several recording techniques and equipment are used in outdoor and indoor recordings for Motion Picture. The choices are usually characterized from subjectivity and technical limitations irrelevant to the desired final sound quality. Our goal is to present results of comparative recordings in order to give answers to every-day-practice problems that arise. Overhead and underneath booming and the use of wireless-lavalier microphones are compared through third octave frequency analysis. 1. INTRODUCTION TO THE PRODUCTION OF SPEECH The articulation of speech is a unique characteristic that separates humans from the rest of the animal kingdom. With speech we communicate and with the use of the same system we sing. The greatness of this system that can articulate so many vowel sounds, consonants (vowels and consonants), syllables (phonemes combine to form syllables) and words in so many languages and dialects with so many accents spoken by humans all over the world, is one of the basic elements of our study. But it is not a topic that we will present in depth, since our problems start after the articulation of speech. Goussios et al. Microphone recording for Motion Picture The vocal organ consists of the lungs, the larynx, the pharynx, the nose and the mouth (the tongue, the teeth, the lips, the soft palate). Air from the lungs passes through the glottis -the opening between the vocal chords/folds- causing vibration of the chords and thus modulates the flow of air through the larynx,which exits from the oral and nasal cavities [1]. The vocal folds are longer and heavier in the adult male than in the female and, therefore, vibrate at a lower frequency (pitch). Frequencies used in speech are 110Hz in the male and 220Hz in the female, with wide variations from one individual to another [1]. Speech and singing are closely related functions of the human voice. Male opera singers control their voices from D2 to D5 (73-587Hz / from Bass to Counter Tenor) while female from C3 to F6 (130-1396Hz / from Alto to Soprano Coloratura). These singers use six different voice resonators of the human body, which are the chest, the oral cavity, the forehead, the nose and nasal cavity and the top part of the head. If we were to record a singer or even a speaker (actor, interviewee etc), questions that arises are on the percentage of the contribution of all these resonators on the final result. For example, the difference of recordings performed closer to the chest from others closer to the forehead, is a quality and quantity value under study. It is interesting that some human sounds, such as nasalized vowel sounds, are made by allowing sound to exit through both the mouth and the nose. 2. SOUND FOR MOTION PICTURE Sound for film and television supports the story of a narrative, documentary, or commercial film or television program. Dialogue and narration -if any- have a direct storytelling role in filmmaking: they tell the story. As a matter of fact, human voices are usually the most significant elements of this sonic construction: the sound track. Dialogues are usually recorded by the sound personnel that can be one or more persons. The typical sound crew for a film production consists of a Production Sound Recordist and a Boom Operator. The production sound recordings are used in post production for the final sound track. Microphones can be categorized in different types by the methods of transduction applied on their design and construction, and also by directivity, polar patterns and characteristics. Of course they can be divided into other groups by means of other characteristics. Since this study is concentrated on outdoor and indoor recordings for motion picture and focuses on the recordings of human voices-dialogues, the two basic types that we are about to use and examine are directional condenser microphones and lavalier (wireless/RF/clip/personal) microphones, which are the most frequently used transducers for these applications. This doesn’t mean that other types of microphones are not used for film and television purposes. 3. MICROPHONES & MICROPHONE TECHNIQUES 3.1. A short introduction on film applications – Directional and lavalier microphones It is generally desirable to keep the diffusive field level low in recording, since it is very difficult (practically impossible yet) to reduce reverberation in post production, while it is very simple to add it. Directional microphones help on that direction since they exhibit forward preference for sound and suppression of reverberation. Microphones with hypercardioid and supercardioid polar patterns have a distance factor of 2.0 for pick-up of reverberation compared to a pressure microphone [2]. Regarding directional microphones, the design and the length of the interference tube lead to better directional discrimination of the microphone; and usually, the more discriminating it becomes in rejecting off-axis sound. The tube is slotted and this creates a phase difference for off-axis arriving sounds, resulting in cancellation and reduction through interference. The discrimination is frequency dependent: most effective for wavelengths shorter than the interference’s tube length. These slots are covered with acoustical resisting material and the end of the tube terminates in a transducer. Sound waves progressing along the axis of the tube reach the transducer unaffected. Sound incident on the tube from 90o for example, will suffer interference effects within the tube and will not add together at the transducer. In sum, there is an increase in directivity with an accompanying reduction of the diffusive field level and off-axis arriving sound. These characteristics make directional microphones ideal or at least preferable than the rest, for film applications, especially dialogue recordings on location [2], [3]. AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 2 of 7 Goussios et al. Microphone recording for Motion Picture What really happens is that the sounds that arrive from different angles are attenuated and “colored”. The timbre is quite noticeably changed. In case the microphone is not in the correct position at the proper moment in order to record an actor, the actor’s voice is off-axis and sounds off-mike (the voice thins and the frontal presence falls away). And that is a difficulty in the use of the directional microphones which must be used from boom operators with great respect to their radiation characteristics. Also other sounds recorded simultaneously with the actor’s voice -footsteps for example- are noticeably colored [2]. Lavaliers due to their small size and weight are often used for single camera operation. The sound quality is average and their response on lower frequencies relies on the proximity effect attempting to gain some low frequencies from the resonance of the chest cavity [3]. These microphones are also used in cases when the directional microphone cannot be placed because of technical limitations. 3.2. Microphone accessories Two of the biggest problems that occur in outdoor recordings are vibration and wind. An effective way to control both these problems is the use of the combination of a pistol-grip shock-mount with a basket windscreen (zeppelin). Additionally a hairy coat windscreen can be used [4]. Wind susceptibility is relatively high for directional microphones. This is why windscreens must be used to create a protected area around the microphone. Since this is not just wind noise but rather an added interaction between the wind and the microphone (which is difficult if not impossible to remove in post production), care must be taken. Basket windscreens create around the microphone a volume of air having low turbulence [2]. Even fast movements and panning of the microphone on the fish pole can lead to unwanted noise due to the passing of air through the interference tube’s slots. This is why the use of the foam windshield is recommended even in quiet shooting stage settings to avoid such unpleasant surprises. The slightest breeze (even if it is indirect and man made) can cause sound interference. To avoid wind outdoors, a hairy coat windshield can be used which offers, according to its manufacturer, increase of the wind damping of the windscreen by 15dB. 3.3. The use of microphones on the set Experience is the only guide as to how much one person can achieve without compromising the intelligibility/fidelity on the recorded sound [3]. The principal responsibility of the boom operator is microphone placement, usually using a boom pole, which allows precise control of the microphone at a distance away from the actors. He or she will also place wireless microphones on actors when it is necessary. Boom operators must know the exact dimensions of the frames, in order to avoid placing the microphone or boom pole in the view of the camera. They must also have in mind lighting, in order to keep the shadow of the microphone and boom pole from being seen on any surface or any actor being filmed [4]. Frequency response is depended on distance from the microphone. Also increasing the distance between a sound source and a microphone, decreases direct sound and since the diffusive field remains constant this results on a relative increase of the reverberation (atmosphere, ambient noise). As mentioned before, and since it is practically impossible to reduce reverberation significantly in post-production, it is desired to record a sound source relatively close. What must someone have in mind, when operating the boom or generally recording for motion picture, is that the microphone-actor (sound source) combination obeys the Inverse Square Law. This means that if the desired “close” position can be achieved, it has to be the same for all the recordings of the takes of the scene and the same after all the movement and panning while recording different actors. The closer the distance the easier it becomes for the level to fluctuate and experience deeps and peaks in the sound pressure level. 4. MEASUREMENTS 4.1. Introduction For the needs of our study we performed many sets of measurements. The first/test measurements were done in order to find out which are the appropriate signals to use and also to decide about the setup, its parameters and its elements. Apart from the disadvantages of the primary setup (intense frequency deep due to the crossover frequency), it is clear from the very beginning that there are quality and quantity differences almost AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 3 of 7 Goussios et al. Microphone recording for Motion Picture between all the different microphone accessories that can be used. the use of foam causes a downward slide of the response. 4.2. 4.3. Test Measurements General Measurements 4.2.1. Set up details 4.3.1. Introduction The test measurements/recordings that were performed, aimed to concentrate on and define the differences of the microphone response due to the use of the foam windscreen over the microphone, the basket windshield and also their combinations. After the test measurements we proceed in repeating the measurements with the same set up, using two different types of loudspeakers. The set up consists of a CD player, an amplifier, a loudspeaker and a microphone on suspension, a mixer and a recording media (computer). In detail, the elements of the setup are the following: directional condenser microphone, foam windshield, suspensionpistol grip, basket windshield, mixer, stereo integrated amplifier, a two way commercial loudspeaker, CD player and a laptop computer The signals that were used are: White noise (broadband), Sweep (4, 8 and 16sec) and recorded voice. The microphone was placed close to the loudspeaker as if overhead booming was applied for the recording. 4.2.2. Test Results Apart from the inability of the loudspeaker to provide a flat frequency response we gathered some useful issues concerning our research. We concluded on using white noise and frequency sweeps as test signals and record live human voice when necessary. The difference between the results that derive from the use of noise and sweep is less than 0.5dB. Two frequency analysis software applications were used to process the recordings with almost identical results. Apart from the use of directional microphone, a lavalier microphone was used. Overhead and underneath booming was applied to record noise and sweeps. The same recordings were performed outdoors with the addition of the hairy coat windshield. A fan was used indoors, in order to create wind conditions and record the effect of the use of microphone accessories. In a professional studio, simultaneous recordings of two lavaliers and a directional microphone were performed in order to compare the differences that occur due selection of different recording positions and the use of different types of microphones. 4.3.2. General results From the comparative curves of the directional microphone inside the basket windshield and the same combined with the hairy coat (Fig. 1), it appears that the coat is effective in LF and it increases the wind damping of the windscreen by 15dB in 100Hz while starting with 10dB in 31,5Hz. The effect of the LF and respectively wind damping affects the response up to 400Hz (-5dB). The disadvantages of the use of the coat make their appearance at 5000dB (-2dB) progressing to -11dB at 16000Hz. In order to perform these recordings we used a fan to create (quite extreme) wind conditions indoors. Above 2500Hz the use of the foam windshield, the basket and their combination cause significant alterations on the frequency response. These are stronger above the 5000Hz region. What seems to require further investigation is the way the frequency response changes above 5000Hz especially with the use of the basket and the basket-foam combination, while AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 4 of 7 Microphone recording for Motion Picture 0 0 -5 -2 -10 -4 Indoor, wind, hairy coat Indoor, wind, basket -15 -6 Rel Magn (dB) (ref Max) Rel Magn (dB) (ref overall Max) Goussios et al. -20 -25 -30 -35 -40 -8 -10 -12 -14 -45 hairy coat basket foam straight -16 -18 63 00 10 00 0 16 00 0 3rd Octaves (Hz) Comparing the underneath and overhead booming recordings outdoors does not show any serious difference in the frequency response of the two. The recordings were performed with signals and not with a human speaking in order to show any variations in the radiated sound (due to the chest resonance etc.) These curves are just comparing the operation. Underneath and overhead directional microphone recordings (Fig. 3) were also performed in a professional studio with a human speaking. It is obvious from the curves that there is a low and mid frequency preference when using the underneath technique and this can be due to resonances of the human body. The voice is recorded with richer timbre when the microphone is placed overhead. 0 -5 -10 -15 -20 Overhead -25 Underneath -30 Figure 3: Overhead vs Underneath AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 5 of 7 63 00 40 00 10 00 0 16 00 0 3rd Octaves (Hz) 25 00 16 00 63 0 10 00 40 0 25 0 16 0 63 10 0 40 -35 25 From the same comparative curves of the directional microphone placed underneath the loudspeaker, it appears that the effect of the different accessories is close to that applied on the overhead microphone setup. It is obvious that the microphone when used straight is more acceptive of the high frequencies, but as commented above, what seems better, when moving and panning the microphone for the needs of a film production, is to use the basket, or the foam windshield, with the last appearing high frequencies filtering (34dB). Figure 2: Straight, foam, basket and hairy coat comparison, overhead setup Rel Magn (dB) (ref Max) We performed recordings of measurement signals outdoors with the directional microphone placed overhead the loudspeaker using the windshield coat, the basket the foam windshield and the microphone straight (Fig. 2). The weather was not windy. What appears from the curves is a -more or less- equal operation until 1250Hz. The hairy coat demonstrates high frequencies filtering which becomes greater in the region of 8000Hz. Straight microphone presents the better frequency response in the high frequencies, but its use is not recommended without the foam windshield for reasons explained in the text. The microphone was steady while recording and this was an advantage in favor of the straight microphone. What is interesting is the comparison of the effect of the basket and foam in the high frequencies where foam appears to be a lot more dampening than the basket. 16 00 0 40 00 3rd Octav es (Hz) Figure 1: Basket and hairy coat comparison 63 00 10 00 0 25 00 16 00 63 0 10 00 40 0 25 0 16 0 63 10 0 25 -20 40 25 00 40 00 10 00 16 00 40 0 63 0 16 0 25 0 10 0 40 63 25 -50 Goussios et al. Microphone recording for Motion Picture In the same studio a lavalier microphone was placed on the center of the actor’s chest while another identical microphone, on the left. There aren’t any noticeable differences on the response apart from preference of the center position lavalier in the region of 6300Hz. Afterwards a lavalier microphone was placed on the right of the actor’s chest and under his clothes while the other remained in its symmetrical position, on the left. There aren’t any serious differences on the response. What is noticeable is that after 3150Hz a fluctuation in the response is obvious that might be due to the clothing, but cannot be commentated at this particular instance. From the comparison of overhead directional microphone recording and the recording of the lavalier microphone (Fig. 4) it is obvious that the sound recorded with the lavalier is concentrated in a mid frequencies region. The recording of the directional microphone is wider resulting in more realistic sound concerning the timbre of the recorded voice. Simultaneous recordings of directional microphones placed overhead and underneath were not performed, and generally the possibility of synchronous recordings from two directional and two or three lavaliers, would probably lead to more accurate results. It is ideal to repeat these recordings and measurements in an anechoic chamber with the parallel existence of a continuous and simultaneous reference of an omnidirectional microphone with flat response and this is part of our further work. It would be interesting to suggest post-production solutions, when different techniques are applied on the set, in order to unify the recordings and smooth their differences. 0 -5 Rel Magn (dB) (ref Max) conclusions concerning the differences between the basic microphone applications that are used in motion picture productions. The quantitative differences can give a first impression to those interested and involved in film sound. These results can be also used for educational reasons, since anybody can imagine the existence of differences in the different applied techniques, but the changes -which are audible-, are not that often presented quantitative. -10 Subjective tests can also be carried out to find out the percentage of the objective differences that are perceptible by humans, and to determine their significance. -15 -20 Overhead Lavalier center -25 Lavalier left 63 0 10 00 16 00 25 00 40 00 63 00 10 00 0 16 00 0 40 0 25 0 16 0 63 [1] Roosing T.D., Moore F.R., Wheeler P.A., The Science of Sound, 3rd edition, Addisonn Wesley, San Francisco, 2002 10 0 -35 40 6. 25 -30 3rd Octaves (Hz) Figure 4: Overhead vs lavaliers From the comparison of the accessories such as foam and basket windshields, obvious differences are not noticed, apart from the high frequencies damping above 6300Hz, due to the use of the high frequency absorbing materials of the windshields. 5. CONCLUSION & FURTHER WORK REFERENCES [2] Holman Tomlinson, Sound for Film and Television, 2nd edition, Focal Press, Boston, 2002 [3] Grant Tony, Audio for single camera operation, Focal Press, Oxford, 2003 [4] Yewdall David Lewis, Practical Art of Motion Picture Sound, 2nd edition, Focal Press, Boston, 2003 The results of the measurements and the comparative curves lead to certain -more or less expected- AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 6 of 7 Goussios et al. Microphone recording for Motion Picture AES 122nd Convention, Vienna, Austria, 2007 May 5–8 Page 7 of 7