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3. Now advance to Track 3. This track contains a set of warble tones beginning at 126 Hz,

moving downward to the lowest frequencies. As this track is played, keep your eye on

the meter. If none of the tones on Track 3 causes an over-reading, draw a horizontal

line on the chart paper at a level of -7 dB. (See Figure 3) This will be your baseline

reference level.

4. If any of these tones causes an over-load reading on the meter, stop the CD player and

adjust the CD source volume downward slightly. Begin the test again, making sure that

none of the segments in Track 3 will cause an overload. Once you have set a playback

level that causes no overloads, return again to Track 2 and note the new level as

observed on the sound level meter; draw a horizontal line on the chart at the indicated

level. For example, let's assume that your new level setting from the CD source results

in a reading of, say, -9 on the meter; then you would mark the chart paper with a line

at -9, which would become your new baseline reference level. (See Figure 8 below)

5. For now, let's assume that your initial setting of -7 dB was OK and that there were no

overloads when you played Track 3.

6. Beginning with Track 4 and proceeding on to Track 26, make entries on the chart paper

for each warble tone. Before each tone plays, an announcer names the frequency of the

tone. You will note that the warble tone sequence begins at the highest frequency of

126 Hz, progressing downward to the lowest frequency of 20 Hz. Make your entries by

putting a dot on the intersection of the announced frequency and the level as you read

it on the sound level meter. This process is shown in Figure 9. Note that the test tracks

are about 35 seconds long -

probably longer than you will

actually need to make an

entry. You may speed up the

measurement process by

pressing the skip button on

the CD player once you have

made your entry on the chart.

During the course of making

your entries, you may observe

that the meter reading shows

a uniform flickering between two adjacent values. If this occurs consistently, it indi-

cates a value halfway between the two LED's, and you may make your entry according

ly at a half-dB step.

7. After you have finished plotting the sequence of readings, simply connect the dots. You

are now ready to interpret the plotted data with the help of the following sample plots.

-5dB

-6dB

-7dB

-8dB

-9dB

10dB

11dB

12dB

14dB

16dB

20Hz

22 24 25

31 35 41 45

62 68

76 85

95 105

115

126

Figure 8

0dB

-1 dB

-2dB

-3dB

-4dB