| Recording Tip#17 |
| Recording Basics Part 4 |
| Peak vs. Average |
| Bob Dennis and Daniel Dennis |
| What Format? |
| In the last tip, we covered preventing overload. Although the procedure for setting levels is pretty much the same for digital and analog, there is one major difference which can make all the difference. |
| In analog recording, we are pretty much concerning ourselves with average level, which equates to how loud it sounds to the human ear. This is read accurately on a VU Meter (the top meters in the diagram below). |
| In digital recording, we are only concerned with peak energy - or in other words, the highest level of an audio waveform, no matter how long it lasts. A peak can last for a hundredth of a second (or far less), and still cause significant overload. A meter which reads this level is called a peak meter or a peak-detecting meter (these two terms mean the same thing). The bottom meters in the diagram below are peak detecting meters. |
| Peak vs. Average |
| The Digital Recorder and Its Levels |
| Much of the professional recording done today is done in digital formats. In the digital recorder, the audio signal coming in is measured several thousand times a second (usually between 44,100 times a second and 96,000). Each time it is measured, the audio signal level is assigned a number to define the level. Pulses are then recorded onto the tape, which represent the numbers. Since the audio signal levels are converted to numbers, the recorder is called a digital recorder. Digital tape recorders have the distinct advantage of having no tape noise and of copies sounding like the original. |
| Digital recorders cannot tolerate any amount of overload. When the signal coming into the recorder is too high, the machine runs out of numbers to define the audio level. The result is immediate and severe distortion. The recorders are sensitive to the peak energy of the highest crest of the waveform and the digital recorders meters read this peak energy. The console meters usually respond to the average level of the waveform, which determines how loud it sounds. |
| There is can be quite a difference between the peak energy of the waveform and the average level of the waveform. Instruments like bass guitars have low level of peak energy compared to the average level. Instruments that are percussive, like drums and cymbals, have a great amount of peak energy. |
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| Correct Digital Recorder Levels |
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| After you adjust the console for the correct levels at the console input and output, you will have to adjust the levels so that the machine's meters read about "-6." The lower level of "-6" is used to provide room for an unexpected peak to occur and still not go over the "0" point. If any peak goes over "0" it will be severely distorted. To get the digital recorder's meters to operate, you must arm tracks that you are going to record. When the tracks are armed, there will be a flashing red light under the track meter and you will see the input-signal peak-level on the tape machine's meters. |
| You will find that the levels of percussive instruments, such as drums and cymbals, will have to be turned down. The console meters may read as low as "-10" when the levels are adjusted to the correct level for the tape machine. To reduce the level for these instruments, reduce the main channel fader below the 75% area. The console meters may read as high as "+3" for melody instruments such as bass guitar, to get the correct levels for the digital recorder. Change the main-channel fader position to slightly above the 75% level as necessary to get the proper recorder levels. |