Mark R. Johnson


[Interactive Screens]
[Amateur Recording]
[24 Hours]




Amateur Recording
Part 3. Endemic Noise

Endemic noise is electrical noise that is internal to the system itself. It can include such things as tape hiss, faulty connections, electrical hum, EMF interference, etc. Essentially, whenever you add anything to the circuit, whether it be a new device or simply more cable, you will inevitably be introducing more noise to the system. Sometimes it can be reduced through careful tweaking of the equipment settings, but often it is unavoidable.

In some cases, the source of such noise can be difficult to nail down. For instance, in any electrical equipment in the United States, you can almost always identify a 60Hz signal, caused by the cycle rate of the AC current. Audio equipment manufacturers will often do their best to remove this artifact, but as long as the equipment is plugged into an outlet, it will usually surface in one way or another.

One should always make sure that all of the cable connectors tying the system together are fully locked in place. Loose connectors are often the cause of attenuated or crackling signals. Also, loose connectors can sometimes cause EMF interference to be picked up. Essentially, if there is a small gap between the connector and the plug, it can begin to act like a capacitor, which is what one uses to tune in radio broadcasts.

In general, all electrical equipment will exhibit some level of just random noise. It is not always clear what causes this basic noise level (temperature, radiation, cosmic rays?), but it is almost always present. The most obvious example of this can be heard by plugging a pair of headphones into a mixer with no inputs connected. Turning up the volume will reveal quite a bit of noise.

Similarly, magnetic tapes also have an inherent level of noise, commonly referred to as tape hiss. One of the great advantages of digital audio tapes, however, is that this tape hiss does not get mixed into the audio recording. This is because the signal actually stored to the digital tape is composed of only digitally ones and zeros, not the analog waveform of the audio. The ones and zeros, therefore, can use the full dynamic range of the magnetic tape to provide very clear and obvious separation between the signal and the underlying noise. Analog tape, however, ends up mixing the tape hiss with the analog audio signal destroying some of its fidelity, as shown in the figure below:

[Diagram of digital vs. analog tape]
Noise due to tape hiss has little effect on a digital signal,
but has a strong effect on an analog signal.

What To Do

The best way to cut down on endemic noise is to keep your system as simple as possible. As mentioned before, every component added to the system adds noise. Start off by only connecting up components that are necessary to the recording.

Also, make sure that all of the components are operating at their nominal level. Most components have to adjust the audio signal internally for processing. Each device is designed with a nominal signal range -- a signal level range in which the device operates best, introducing the least noise and fewest unwanted processing artifacts. By ensuring that all of the components of the system are operating within their nominal range, you can greatly reduce the amount of noise in the system. Often, this may take a lot of careful tweaking of the various knobs and dials to find the right balance among all of the devices in the circuit.

Finally, while processing the audio, try to avoid excessive generations of taping. Each time a signal is processed and recorded, an added fraction of noise is recorded with the signal. If the same signal is reprocessed several times, the amount of noise and grow significantly. A common practice is to use a duplicate of the original recording to perform any testing or multiple reprocessing. Once a final method is chosen for the processing, then go back and run through the procedure drawing from the original master. In doing so, try to optimize the procedure to remove or combine as many steps as possible. Of course, be careful to hold on to all of your master recordings. You don't want to sacrifice them during the processing, just in case you need to go back to them later on.

[Table of Contents] [Next Report]
    [Return to Top] Copyright 1997, Mark R. Johnson.
Last modified 4/26/97.