RCA signals

[sbayeta]

Hi,
Can anyone please tell me the levels of RCA audio signals ? Also, I'd like to know if the signal is referenced to the equipment ground.
Thanks a lot

 

[Sebi]

RCA (or cinch) only a type of connector, no standard for audio level. (most of case the video in-out also RCA)
Some help if marked e.g. mic.-in, line in, tape-in, but the exact level readable only from device spec.
Try connect the audio-source, and when the output haven't distortion, the level is good. If the output volume too low, the input signal weak for input.

 

[sbayeta]

Thanks for your reply.

I understand what you're saying, but there must some de-facto standard for the audio signals that use RCA connectors, since you can buy a cd player, tape player or FM receiver from any vendor and connect it to any other vendor amplifier without worrying about the signal levels, the impedance, or the grounding, right ?

 

[Sebi]

Yes, don't worry, just connect it.

 

[sbayeta]

Hi again,
I need to know the signal levels, ground reference and impedance because I'm working in a little project, which has an audio interface.

Thanks

 

[stevez]

As stated by others, the connector does not define the signal level. RCA connectors are often used on what I've come to understand is "line-level" outputs or inputs. I think "line-level" is 1 volt peak to peak - at least that is what I have come to understand.

 

[Noggin]

You DO have to worry about levels and such when you're buying audio equipment.

My head unit in my car has 4v pre-outs (RCA's)
My amplifier has adjustable inputs, 250mV to 8v. There is a gain control knob, I set it to 4v to match my head unit.

 

[pebe]

As stated by others, the connector does not define the signal level. RCA connectors are often used on what I've come to understand is "line-level" outputs or inputs. I think "line-level" is 1 volt peak to peak - at least that is what I have come to understand.

I seem to remember that line level audio is 1mW into 600ohms. I may be wrong because I've not used it for a long time.

 

[stevez]

I found a site (actually refers to WABC radio station) and there was a good explanation of "line level." The author refers to an obsolete standard though it may be defined in a current standard. Line level was said to be 0.775 Vrms into 600 ohms which is also the basis for 0dBu, a point of reference. 0.775 volts works out to be 1.0975 volts peak (not p to p) and it appears that many users often shortcut to 1 volt peak (which would then be .707 Vrms if it were a sine wave). Interestingly enough other references were made to "line level" as being between 0.3 and 2 volts.

So, if RCA connectors are used as output on an audio device it might be line level (as described above) or it might be something else. I noticed numerous web pages on how to deal with the various levels.

 

[unclejed613]

first dBu is dB referenced to 1 microvolt, not 0.775V. dBu is used for measuring noise levels.
a more convenient reference for line level is dBV, or dB referenced to a volt.
usually (but not always) an amplifier has it's gain set so that 1Vrms drives the amp to it's rated output. this number varies from manufacturer to manufacturer, but 90% of amplifier manufaturers set the gain of the amplifier to be at full rated power with 1Vrms in. so for a 100W amp, where 100W=28.3Vrms into 8 ohms, sets the amp gain at 30 (this of course does not include any level controls on the amp, which for high end audio and pro audio, usually don't exist).
so this is a de-facto industry standard, but not everybody adheres to it.

so the answer to the OP is that most of the industry considers 0dBV (1Vrms) to be the "standard" line level. at an average listening level, you probably have more like 100mVrms on the signal lines. some preamps go as high as 3 or 4 volts out, but that's overkill