|NSS Home Page Nature Sounds Newsletter Spring 1995 Equipment Review|
by Clay Reeves,
Film & Nature Sound Recordist from Colorado
In this day and age of modern technologies, it is increasingly important for the sound recordist to completely understand and apply the recording equipment with maximum skills. Two types of formats are perhaps the most popular for wildlife and environmental sound recording. They are analog and digital, digital being the newest at about 10 years of age. My experience has been in both analog and digital, and the following review is based on the current equipment now being used.
Analog tape recorder - Nagra N-S. Without reservation, the finest analog recorder made for this format. The machine is very portable, extremely rugged, and designed by Swiss craftsmen. The recording format is 1/4" tape stereo; however, a front switch allows for mono input. Standard reel size is 5", but the optional frame/cover permits 7" reels. A roll-off filter is standard, with 6 position selections, individual channel level controls, tape/direct switch permits on tape confidence monitoring, input controls for microphone or line, headphone input/level control, and adjustable phantom power selections for both 12 volt and 48 volt mics. A peak modulometer meter is standard, and well-lighted for night recording. The main control lever allows for a choice of off, test, record (with and without +4dB limiter), and playback (with and without loudspeaker). Line outputs are standard, and there is a noise reduction switch for those choosing to use some form of noise reduction, such as dbx or Dolby SR. Not mentioned are many other features too numerous to document. The basic power is 12 each "D" size alkaline batteries. It is my opinion that this power will operate the Nagra for about 18 hours or many several inch reels of tape.
While the above discussion points out many impressive features, the greatest value of this recorder is its ability to reproduce very accurately the sounds of wildlife and environment. The Nagra was designed for motion picture soundtracks. Its precise speed, very flat frequency response (30Hz - 15Khz +/- 1db at 7.5 IPS), and a signal-to-noise ratio of 72db make this the standard for recording. For greater S/N ratio there is a 15IPS setting. The preamplifier circuit of the IV-S is unbelievably clean and natural, a very important point to consider when using high output microphones such as Sennheiser MKH Series.
The real test of this machine is in the field. Setting record levels can be done in the test position, then switching to record and monitoring off-tape to protect against overmodulation or distortion caused by birds with very high transient voice calls. The peak modulometer shows instantaneous peak levels, which allows the recordist to make immediate level setting corrections. While this is a fantastic recorder, there are some drawbacks to consider. First, the price of a new IV-STC is about $12,000. A good used IV-S is about $6000. Secondly, the total weight, with tape and batteries, is about 16 pounds. As with any analog recorder, there is a certain amount of tape hiss associated with tape/head contact.
However, with the introduction of Scotch 966 mastering tape, the hiss can be greatly reduced. This tape is a high-output, low-noise recording tape. It is designed for full frequency recording, such as found in recording studios for singing and musical groups. It is a dramatic improvement over previous voice tapes, such as 208 or 808. My recommendation is to use 1.5 mil thick tape. This will preserve the final integrity of the recording by preventing print-through and tape stretch. To shoulder the burden of the Nagra's rugged features, it is recommended to purchase the Porta-Brace Nagra case. The case is designed with full protection to the equipment, has generous pockets, and a very comfortable shoulder strap and waist belt.
Microphones - Sennheiser MKH Series. The age of digital is here and many manufacturers are now introducing new products which are designed for this format. Sennheiser has introduced the MKH series microphones with some amazing results. These mics are of the condenser design and are powered by a phantom source such as 48 volts. There is a broad selection to choose from, the MKH-20 (omni directional), MKH-30 (agure-eight), MKH-40 (cardiod), MKH-50 (supercardiod), MKH-60 (short shot gun/lobar), MKH-70 (long shotgun/lobar), and the MKH-80 with switchable pickup patterns. This discussion will be limited to the MKH-40, 30 and 70 designs.
The MKH-70 is a great shotgun mic. It is very lightweight (6.4 ozs.), extremely high output (50 MV/Pa(-26dBV), and is very natural sounding. The mic has a low cut filter (-5dB at50Hz), a switchable presence (+5dB at 10KHz), and switchable pre-attenuation of 10dB. As with all MKH Series mics, there is no transformer. The mic is also designed for RF interference resistance. Because there is a small lobe (about 5dB at 180°) this mic produces a very natural sound. Keep in mind this mic has very high output and must be mounted in a good windscreen (Zeppelin Style) to perform properly. Hand noise can be a serious problem as well as cable noise. Because of the lobe pattern, the hull points are at 120°. This means that the lowest signal reception will occur at 120° instead of 180°. The MKH-70 has an equivalent noise level of 8dBA, the lowest in the industry.
Using this mic in the field is a great pleasure. Its lightweight, totally humidity-proof construction, and impressive sonic clarity make this unit a great shotgun for birding. The best way to use this mic is point it directly at the source to be recorded. Then try to position yourself to use the nulls at 120° to eliminate unwanted background noise. Because of the high output, any noise behind the subject recorded will probably find its way to the tape as well. Also, this mic will tend to quickly overload the preamps of some digital recorders, causing serious absolute distortion.
The MKH-40 is the cardiod design, much shorter in construction than the MKH-70, and with slightly less output (25MV/Pa(-32dBV). The MKH-30 is the figure-eight design, about the same output. When mounted together, this combination makes a great MS stereo package. MS means mid-side and has many advantages over other coincident techniques, is mono-compatible, and an extremely high quality M-S signal/system can be assembled from the MKH-30, 40 mics. The mics are clipped together in "piggy-back" style and aligned with the capsules in the same plane. Because of the way the pair of microphones responds to reverberant information, a well-done M-S recording preserves a high degree of realism. When using the M-S technique, the mic system can be positioned in order that the forward-facing capsule produces the optimum mono-signal with the best possible frequency response while maintaining easily adjustable stereo perspective and ambience.
X-Y techniques can suffer from center mic high frequency deficiency caused by off-axis degradation of HF response of many directional mics. Also, recordists may be disturbed by the phasing effects caused by the movement across the faces of improperly positioned mics, and by the fact that images at low frequencies are often narrower than those at high frequencies. The M-S technique uses a cardiod mic (M) aimed along the central axis of the sound source and a figure eight mic(s) at right angles to this axis.
The outputs of the mics are combined in a "sum and difference" matrix amplifier to produce conventional left and right stereo signals. By correctly positioning the (M) mic, an optimum mono signal can be recorded with a minimum of off-axis coloration. After matrixing the (M-S) signals, the results are equivalent to AH X-Y stereo signal. The matrix process adds and subtracts the M and S signals to increase or decrease the spatial result of the stereo signal. When the M component is increased, the spread is narrower; when the S-component is increased, the spread is wider.
To direct the output of an M-S pair to any position within the final stereo recording, the outputs of the matrix amplifier are mixed into the final L-R stereo signal. For an example, if a bird is being recorded in a sitting position, the M-S system would position that bird at or near the center of the sound field, assuming the (M) mic is pointed at the bird. When the bird flies away (the mics not moved), the bird would move across the sound field in a very natural fashion, such as heard by the human ear. There would be no "hole pattern" as typically associated with X-Y recording techniques. The recorded signal may be recorded as a mono-signal without any phase shifting or cancellation. In conclusion, great care must be taken not to rotate the mic pair about its longitudinal axis. Monitoring the final result through high-quality headphones can allow the recordist to professionally set up the spatial reality of the recording.
M-S Matrix Encode/Decode-PortaFlex ADO66-11 To properly mix the final M-S recording, a matrix Encode/Decode "Black Box" must be used. The PortaFlex ADO66-11 is a high quality, portable, stereo mic pre-amp with double matrix decoder. The unit operates on nine AA batteries, has four separate inputs, switchable high pass filter, 12v - 48v phantom power unit, and course and fine level controls. The fine control is ganged for stereo or available as separate gain. There is a LED meter for each stereo channel, a phase correction switch, and a switchable matrix encode/decode amplifier. Also, inputs and outputs are balanced XLR connectors.
This unit has a six-position switch that allows the recordist to monitor separate mixing/decoding options while in the field or in final post-production. The instruction manual is very well written, with all functions clearly detailed and explained. All functions and features are identified by a series of illustrations of the actual unit. With the Portaflex, the recordist can mix recordings in the field and then record the final resultant in either X-Y stereo or mono. The mics connect directly into this unit, then the output is sent to the inputs of the recorder. The signal can be mixed prior to actual recording. The course level controls permit a general level adjustment. By viewing the LEDs for each channel, the fine level controls can be used to "supertune" the final mix before recording.
Because the unit is capable of 80dB max gain, caution must be exercised not to introduce distortion caused by overmodulation. Also, it is only by experience that the sound recordist will learn the proper spatial settings, as headphones tend to create a narrow appreciation of the spatial reality as opposed to the real settings required. This unit is a welcome addition to a recording system utilizing high-quality components. It is lightweight, compact, very feature-rich, and provides a much needed opportunity in the field to create very professional recordings with little experience. Somewhat pricey at $1,200, it is worth its weight in gold.
Digital Tape Recorder - Fostex PD-2 As explained earlier, the digital world is here and the recording format of preference seems to be "DAT." Digital Audio Tape is a small,compact cassette-style cartridge with recording times now up to 120 minutes. The Fostex PD-2 is a RDAT stereo recorder which was designed to compete with the Nagra IV-STC recorder in the motion picture industry. It includes true time code, is about 11 pounds in weight and is the elite of DAT recorders at $12,000. The machine is designed somewhat like a Nagra, at least, in the positioning of the controls. As with all DAT recorders, there is no tape hiss, and the equipment tends to have superior performance specifications, sometimes very misleading. DAT recorders do not record the actual signal as heard by mics. They rely on analog to digital convertors to create a mathematical reproduction of the real signal. This signal is then sent to the digital tape. Also, digital recorders will not tolerate any overmodulation (max recording level is called absolute) commonly associated with analog recorders.
The Fostex PD-2 has been on the market about 4 years. It is very software-driven and has proven to be very reliable in use. The PD-2 is designed to provide easy operation during use. The front panel contains the viewing screen and its LCD (Liquid Crystal Display) indicates all vital operating parameters: frame rates, audio levels, error IDs, PLIOs, sampling frequency, SMPTE timecode status, A-time readout, battery status, and reference level. The screen is very well lit for night recording, backlit and adjustable. The many level controls are located to the right side, and are ganged or individual for each channel. Switches for record monitor, meter monitor, MS/AB headphone selection, mono/stereo, limiter, and light on/off are among the important features which will command frequent usage. There are VIEW OF CONTROLS ON FOSTEX PD-2 16 function keys that provide many individual call-ups and read outs, which will not be discussed here. A battery check key shows battery voltage under any condition.
Because the Fostex is powered by a NP-IB battery, the life of this battery is about 70 minutes maximum. It would be advisable to have spare NP-IB batteries available or go to a larger, external 12-volt battery system and connect it into the external power port on the side of the unit. The PD-2 is designed to offer a reasonable amount of protection from rain and water. Likewise, the tape transport is sealed from the elements and employs an internal heater that is switched on and off from the front panel. Should moisture enter this area, the heater will automatically switch on and evaporate the moisture that has gathered inside. This is an important feature, should the recordist travel to a high-humidity area such as the Central American rain-forests.
Of particular interest is the fact that the PD-2 has 4 rotary heads and allows off-tape "confidence" monitoring during recording. It uses two 16-bit digital audio channels.
Sampling frequencies are selectable at 48 KHz, 44.1KHz, and 44.056 KHz, the first two being more popular. Analog inputs include balanced mic and line, and each has selectable phantom power (T12 or 48 volts or off), phase reverse, pad switches (V1, V2, M, and flat), attenuation switch (OdB, 15dB, 30dB). A balanced 3pin XLR connection is located on the side panel below the analog inputs and permits digital inputs conforming to consumer (SP DIF) and professional (AES/EBU) of IEC 958. When a digital signal is detected at this connection, the word "digital" will appear on the LCD screen. A limiter is very effective and is a VCA circuit with the threshold set at 10dB below 16-bit full scale level. A compression ratio of 1/3 is applied to signal levels above this threshold. A display on the LCD screen indicates the level of signal compression being applied.
The clipboard software offers full subcode address capability, including start IDs, ELID IDs, PNOs, blank search, and error IDs. Sub IDs are important in order to mark areas of the tape for a later recall. The error ID function flags any questionable recording for you to review later or right away. The rewind is excellent, rewinding at nearly 50 times faster than analog.
One very interesting feature of the PD-2 is the LCD reference markers for adjusting recording headroom. Typically, DAT recording headroom is 18dB. On the PD-2, the headroom is adjustable from -18 to -12dB. While adjusting the maximum output level, the input and output amplifiers' gain is switched automatically. For example, with the reference marker set to -18dB (+4dBU ref. record level) the maximum output level is +22dBU, and the headroom is 18dB. The reference markers are displayed on the LCD screen. Analog outputs are balanced XLR 3PIN connections and are located on the opposite end panel from the inputs. For digital output, a XLR 3PIN connector is located below the analog outputs and for outputting PCM audio conforming to the consumer (SP DIF) and professional (AES/EBU) of IEC 958. Specifications include frequency response (20Hz-20,000 Hz +/- 1.0dB), dynamic range greater than 90dB, wow and flutter less than .002%, and THD less than .05% at 1KHz. Finally, the unit design includes a 4-motor transport that has eliminated the need for complex linkage and belts. Operating controls are well placed and function effectively. For those who have never recorded in digital format, the experience is very much like that of analog. The big exception is that analog has a "forgiving" nature when it comes to overmodulation or distortion. Digital does not. In fact, recording levels that are excessive and go into the "absolute area" will be recorded as total distortion, very harsh and unacceptable. A certain amount of time and experience will be required to properly adjust the record levels for obtaining a good-quality recording. The limiter system will help control the overload recording.
With no tape hiss,it is much easier to record at a lower level and achieve the same results. Care must be given to recording at a very low level because the digital is a mathematical reproduction of the analog signal, and if levels are very low, the machine cannot distinguish which levels to sample, hence a very poor, erratic signal will be recorded. Likewise, when recording with any DAT recorder, remember that a rotary head is rotating and drawing a larger amount of power, thereby reducing battery life. Recording in stop mode with the unit switched on will reduce power consumption, but will require about 2 seconds of time when the record switch is activated to bring the recorder up to speed.
The fascination of solid-state circuitry, LCD viewing screen, and an onboard computer reproducing a large array of features and functions, has made recording with Fostex an extreme pleasure. While slightly less in weight than the Nagra, it is very portable, and is capable of producing very high-quality recordings. Its high-end digital to analog converters and very clean preamplifier circuits really are apparent when playing back recorded material. As with other digital recorders, the sonic quality of the recording tends to be somewhat harsh and bright. This was not evident at all with the PD-2. In fact, the quality was very natural, with a high degree of duplication, just like the analog signal. There are several drawbacks to consider. First, the high cost of the PD-2 at $12,000 limits its accessibility to everyone. Secondly, it requires a substantial amount of power - not a problem if you plan ahead with extra batteries. Finally, it requires a lot of practice to play with the recording levels to obtain distortion free recordings. In conclusion, the more you use the fostex, the more you will appreciate its existence as a really great piece of gear for wildlife and environmental recording.
Articles from Spring 1995
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