Dolby Laboratories CP650 Installation Manual download pdf (Page 98)

Dolby

CP650 Installation Manual Final Adjustments

7-14

Level and Frequency Response

A failure is indicated if a new frequency response measurement of any channel (L, C,

R, Ls, Rs, Bsl, or Bsr) differs from the saved reference measurements by more than

±3 dB. The measurement is taken in the region between 200 Hz and 5 kHz.

A failure is indicated in the Subwoofer channel if the frequency response deviates by

more than ±5 dB from the reference reading, in the region between 60 and 100 Hz. A

change in the sound level from a speaker can be caused by many factors, including:

• Power amplifier gain has been changed, or the amplifier has failed

• Crossover has been changed or has failed

• Speaker has been changed, has failed, has an element with an open circuit, or

is otherwise nonoperational

If the comparison fails any of the frequency response or level tests, a message is

inserted into the event log. For example, in the message R FAIL MH, the R

indicates the Right channel. An L, M, or H represents low-, mid-, and high-frequency

regions. Here, low frequencies are considered to be below 315 Hz, mid frequencies

are between 315 Hz and 2 kHz, and high frequencies are above 2 kHz. If more than

one channel failed the test, multiple events are added to the event log.

7.16.4 Headroom Configuration

Headroom is the difference (in dB) between the highest peaks of the signal and the

highest peak that can be passed through the system without distorting. Use the

Headroom Config setup menu item to specify how this additional capacity is to be

used. The settings available are Typical, Noise Floor Optimization, and

Unity Gain.

Typical (default)

This is the recommended setting. All headroom is available for use by the output

level fader or equalization boost. This setting should not be changed without a

thorough understanding of the consequences.

Noise Floor Optimization

Noise Floor Optimization calculates and utilizes any available leftover capacity in

each channel to improve the overall noise floor of the CP650. It operates by

measuring the extent to which the unit uses the available headroom in the B-chain,

then boosts the overall gain in the digital domain to use all available headroom. The

analog output level trims are then reduced by the amount of that boost, resulting in an

optimally reduced noise floor. This adjustment also factors in the headroom available

to the fader. Changes to the output trim values are transparent to the user, and no

changes will be seen in the fader values in the setup software. Clipping may occur on

high level signals if the fader is set above 7.0.

Noise Floor Optimization mode is indicated by an N in the top right corner of the

front-panel display.

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Dolby Laboratories CP650 Installation Manual Page 98