Manual or auto
Having plugged your sound feeds you must control the level at which they're recorded. Each track usually has the switchable option of manual or auto level. Do not rely on this auto function producing the ‘correct’ level of recorded sound. The auto method of operation is simply designed to increase the channel gain to amplify low level sound, and decrease it for high level sound.
Examples of these two extremes are:
(a) A mic held too closely to a person's mouth will result in the background level falling and rising following the raising and lowering of his/her voice.
(b) Conversely, with a mic at a conventional distance from a person's mouth so that it does not appear in shot, but whilst working in an environment with a varying level of ambient sound, such as a busy road, for example, the overall level will increase and decrease depending on traffic noise, as much as for any variance in voice level.
Both cases will almost certainly render portions of the soundtrack unintelligible and thus, unusable.
Both tracks have individual gain controls associated with their manual position (Figure 5.1). However, do beware that most broadcast cameras have a separate gain control for channel one, often on the front of the camera body (Figure 5.2), or on the viewfinder housing (Figure 5.3). This is in addition to, and in line with, the channel gain control on the recorder section. Ensure you locate it and check that it's fully turned up (see also Section 20, Single person operation: tracks; Sound level). I suggest you also put gaffer tape over it, to ensure it doesn't get altered accidentally. Each channel gain control must be adjusted to ensure that the correct sound level is recorded. But what is the ‘correct’ level, and what form of control can we exercise?
Figure 5.1 Channel gain (level) controls
Figure 5.2 Channel one gain control on front of camcorder body
Figure 5.3 Channel one gain control on viewfinder housing
Level control and dynamic range
The dynamic range of sound in the outside world can be extreme, especially with aircraft, pneumatic drills and heavy traffic to contend with, if all you want to do is to record speech. Although the ear can cope with this dynamic range, it's unlikely that the signal chain we use can accommodate it to its full extent, although digitization has led to an improvement in the acquisition of a wider range than before. But if we are dealing with television, there is still a poor old transmitter between us and the listener/viewer which cannot fully accommodate the whole range.
Moreover, even were the whole dynamic range transmitted, it's most unlikely that it could be heard in its entirety via the replay/receiver due to the average noise level within most domestic environments, if that is, you're working in broadcasting. However, in order for you to provide optimum results, you must understand what is involved in post-production, and the final destination of the finished product – the client/customer/consumer.
Post-production
To take an obvious example, if you are working in a news environment, your recording will almost certainly be used to provide on-air sound without recourse to further processing or dubbing. So it must not exceed the dynamic range of the transmission system, although limiters within the system will ensure no excess level can do any harm. But if you have not adequately controlled your level, those ‘downstream’ limiters may render portions of your soundtrack muddied or unintelligible, and in a fast turnaround environment, the only time this defect is likely to be noticed is when the material is transmitted – ‘Oops, sorry luv!’
If, however, you know that your material will be subject to a dubbing session, then you can leave some of the balance and level decisions to the dubbing editor. To give the editor as much choice as possible, it's best to provide both sufficient level, and as wide a dynamic range as is practical, working within the parameters of your recording format.
Thus, in an ideal world, to competently record sound you need to control the amplified level from the mic via a fader, and to have an indication of the signal strength that you are recording.
Limiter
On some broadcast equipment, a red light on the recorder indicates when the sound level is excessive, and that a limiter is functioning. In order to prevent too high a level of sound being recorded, an automatic cut-off prevents the signal rising above a certain level. A good limiter should act like a ‘soft buffer’ for incoming sound over this level, and not have too hard a cut-off. Thus, if the incoming sound is only just over the optimum level occasionally, the limiter will gently prevent an audible overload, and its red light will flash temporarily. However, if you drive it too hard, with excessive sound levels, the red light will be on almost permanently, and the sound will almost certainly be distorted.
Caution
Many DV cameras do not have a limiter in the audio chain when used in manual, although there is one in circuit when used in auto. Therefore, incoming sound at too high a level will be subject to distortion, if you do not correctly monitor and adjust your input.
Dolby encoding (noise reduction)
This is a deliberate alteration or ‘enhancement’ (pre-emphasis) to higher frequencies within the analogue sound signal before it's recorded, designed to overcome possible losses in quality in the record chain. Amplifier circuitry produces a certain amount of noise (hiss), which increases with the level of amplification applied. The signal carried by the circuit needs to be significantly greater than this background noise, and you will often find a Signal to Noise Ratio (SNR) figure quoted (in decibels) to indicate the level of noise compared to signal you may expect from a piece of equipment. Obviously, the higher the figure, the better!
Unless otherwise requested by production, the Dolby NR facility should always be selected. On Beta SP equipment, the insertion of the SP tape cassette automatically switches Dolby NR in circuit, regardless of the switch position. The sound is decoded upon replay (but not in all camcorders, especially Beta SP). Digital camcorder systems do not use Dolby encoding.