-10 & +4dbu

[breaktheory]

Curious why +4 is considered the professional level. I think I understand the difference but which LE interfaces put out which level - I seemed to be able to find every spec on the interfaces aside from that.

[Craig F]

+4 is usually a balanced connection making it less spectacle to noise and it can run long distances.

-10 is usually unbalanced and not able to drive a long cable

[breaktheory]

When you say long are you talking about like from a recordist booth down to a board?

[Craig F]

1000 ft. vs. 10 ft.

[Darney]

Originally Posted by breaktheory

Curious why +4 is considered the professional level. I think I understand the difference but which LE interfaces put out which level - I seemed to be able to find every spec on the interfaces aside from that.

In professional audio, a popular unit is the dBu. The "u" stands for "unloaded", and was chosen to be similar to lowercase "v", as dBv was the older name for the same thing sort of... the dBV was really a ratio of power gain and level, not voltage. Hence the designation change. It was changed to avoid confusion with dBV. This unit (dBu) is an RMS measurement of voltage which uses as its reference 0.775 VRMS. Chosen for historical reasons, it is the voltage level which delivers 1 mW of power in a 600 ohm resistor, which used to be the standard reference impedance in telephone audio circuits.
The telephone industry is largely responsible for many of the standards used in professional audio. Another good example is that the voltage used for transmission in telephone systems is +48VDC (the battery at the switching station voltage)... the same as the voltage level for phantom powered microphones.
+4 dB is considered by many to be the de facto audio level for professional grade equipment, this equates to 1.23 Vrms into a 50 Ohm load. Thus, as pointed out in the previous post, allows for longer transmission lines, less susceptibility to noise (although this isn't quite accurate, it simply lowers the potential noise floor, and thus gives a better signal to noise ratio).
Since digital systems represent level changes via the number and status of bits that used to encode the data, voltage level has become less relevant and descriptive of the dynamics of a system as a 24 bit system has far more dynamic range potential than an 8 or 16 bit system. Hence the reason that many digital-based systems don't include the "0 dB" reference level - it's a moving target depending upon bit depth. It's more important to understand the noise floor and dynamic range within a system.

[Park Seward]

You will sometimes see the "dBFS" meaning "decibel full scale". 0 dBFS is max level, full scale. Anything higher will clip.

Yes, many standards came from early telephone company work since their goal was to send audio over very long distances with low noise and low distortion. That is where 600 ohms and balanced wiring came from. In fact, some even recommend twisted dry pair as a professional audio interconnect instead of shielded cable.

In Europe, where 48VDC phantom power was developed, the ring voltage is 60-75VAC in most countries. No connection to the development of microphone phantom power.

In 1966, Neumann GmbH of Berlin, Germany, presented a new type of transistorized microphone to the Norwegian Broadcasting Corporation, NRK. Norwegian Radio had requested phantom-powered operation. Since NRK already had 48V available in their studios for their emergency lighting systems, this voltage was therefore used for powering the new microphones (model KM 84), and is the origin of 48-V Phantom Power.

http://en.wikipedia.org/wiki/Phantom_power

[Darney]

Originally Posted by Park Seward

You will sometimes see the "dBFS" meaning "decibel full scale". 0 dBFS is max level, full scale. Anything higher will clip.



In Europe, where 48VDC phantom power was developed, the ring voltage is 60-75VAC in most countries. No connection to the development of microphone phantom power.


http://en.wikipedia.org/wiki/Phantom_power

Ring voltage is unrelated to the 48VDC voltage for transmission in a POTS system. 48V was selected as it's the 'float' voltage of a lead-acid battery, used in telephone switching stations to maintain audio transmission during power outages. Hence the reason NRK used 48V for their emergency lighting systems. The ring and transmission systems are two separate circuits. Basic telephone circuits used a carbon element 'button' microphone that a had a current flowing through the carbon button. Sound waves hitting the carbon granules create a variation in resistance, thereby changing the current flowing through the circuit analogous to the incoming sound... an AC voltage simply would not be usable in the transmission circuitry (unless you really wanted to hear the hum).