Owner`s manual

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Figure 3. The relationship between operating level, clipping and the noise floor.
As you can see, the operating level chosen for any given device has a pretty direct effect on the
working signal-to-noise ratio. Pick a level that is too high and you get premature peak clipping (but
spectacular noise performance). Pick a level that is too low and you have lots of headroom, but a
poor working signal-to-noise ratio. Let’s put some numbers on this: a hypothetical unit, with a -
70dB noise floor, and a +10 dB clipping level.
Right off, you can see that there is a maximum dynamic range of 80 dB (+10 - -70). Now, let’s
explore a few different operating levels. First, we’ll used -20 dB which corresponds to a signal
level of around 0.1 volt. At -20 dB, the working signal-to-noise ratio is 50 dB (-70 - -20), which is
okay, but not spectacular. At this same level, we have 30 dB of headroom (+10 - -20).
Now let’s push the operating level up to -10 dB, about 0.3 volt. See if you can do the math your-
self. The working signal-to-noise ratio is 60 dB and we have 20 dB of headroom. As you can see,
there is always a tradeoff between signal-to-noise and headroom. For our make-believe unit, this
would be a good level to operate it at.
Some manufacturers have been known to specify the dynamic range as the signal-to-noise ratio.
For the unwary person who only looks at numbers without really understanding them, this gives a
truly spectacular number. Only under the most optimistic of operating conditions could the dy-
namic range of a device be construed as the signal-to-noise ratio. The condition under which this is
true is where the headroom remaining is precisely zero dB.
The optimum operating level is a compromise between headroom and working signal-to-noise (s/n)
ratio. For most systems, 60 to 80 dB of working s/n is adequate and practical. Likewise, there
should be at least 16 dB of headroom to accommodate signal peaks. Picking the right operating
level for each component in the system allows you to set the working signal-to-noise ratio/head-
room tradeoff.
Meaning to Signal-to-Noise Ratio