Sony SRP-X700P - Manual (Page 45)

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Reference Level
It is average operating level for input and output of devices.
It can be referred for interconnection. In many professional audio devices, the reference
level is usually set to +4 dBu (or dBm) for balanced signal interfaces of inputs and outputs.
0 dBu or another levels are applied to the balanced one too.
-5 or –10 dBu is applied to unbalanced connector of consumer models in general.
For example, the reference level is designed to output from available output connecters
when 0 VU (being considered to be average operating level) is indicated on output VU
meter, generally in professional devices such as mixer or processor.
Professional products usually indicate its maximum level that could be handled, on such as
operation manual, as well as the reference level for input and output.
Difference between the reference level and maximum level is called headroom which is
considered to be designed at least 14 dB, to avoid unacceptable distortion of peak signals
which can be 8-14 dB higher than average operating level.
RS-232C (Recommended Standard No.232 revision C)
It is one of the EIA recommended standards for interface between computer terminals and
modems. It has been widely applied to computer, printer, etc.
It defined cable length of up to 15 m (2500pF of maximum load capacitance instead of
length, after EIA-232-D), transfer rate of below 20 kbps and voltages with connector of
25-pin D subminiature of unbalanced transmission.
9-pin interface as subset of the RS-232C standard is equipped with IBM PC/AT compatible
machine in standard. And many measuring instruments comply with it.
It has been revised to ANSI/EIA/TIA-232-E.
In SRP-X700P, the D-sub 9-pin for RS-232C is available.
Signal-to-Noise Ratio (S/N Ratio)
It express the difference in decibel between specified signal and noise floor of device or
system. The noise floor is determined by the thermal, digital quantization, etc and is
commonly measured by A-weighted meter.
The maximum S/N ratio is the ratio between the maximum signal level being passed
without clipping and the noise floor.
The S/N ratio can be the ratio between the average operating level (reference level) such as
+4 dBu and the noise. In case adding headroom to this ratio, it expresses dynamic range.
In digital devices, the S/N ratio is the difference between the maximum signal level and the
noise.The dynamic range is about equal to the S/N ratio, in fixed linear system.
Surround Sound
It is sound system to enjoy cinema, containing front speakers fo r mainly spoken lines or
effect, subwoofer for effect and rear speakers mainly for effect sound.
5.1 surround
A representative system is Dolby Digital developed by Dolby Laboratories, consists
of discrete channels for front speakers of left, center and right, rear speakers of left
and right, and subwoofer. It is applied digital audio compression technology. Good
channel separation is realized due to discrete recorded channels and process in
digital.