what is the 0VU point on logic pro meters?

ProTools HD uses fixed-point numbers for its signals, if you use their HDX system. Due to the restricted dynamic range of that representation (just ~144dB for 24 bit), they need to define a virtual headroom. They've chosen -18 dBfs, which is well done, since their interfaces have maximum output of +22 dBu, so at -18 dBfs, the output is +4dBu, the typical studio line level. This way, a ProTools system has a headroom of about 18 dB. Logic uses a floating point mixer, which has about 1500 dB dynamic. In a typical scenario, where 1.0f is 0 dBfs, about 750 dB headroom is available. So, Logic doesn't need that kind of artificial headroom, as you can never overdrive the mixer. If your bus level is too hot, just scale it down with a gain and you're set.

Hope this helps,

DaCaptain

Conway Tokyo wrote:

but I know this isn't true because the meters max out at +6 when in the red.

Talking about "signal level" in audio production is like opening a can of worm.

Lots of standards, lots of information, lots of mis-information, lots of confusion.

For example, you made the following statement: "... but I know this isn't true because the meters max out at +6".

You have to be careful if you talk a bout meters of faders. The meters do not max out at+6dB, the max Fader position is +6dB.

Let's look at the Faders and Meters:

Faders:

The scale next to the Faders represent the position of the Fader, which is technically an I/O device. Its dB scale represents a ratio (how much signal came in vs. how much did get out when passing through that Fader component). The position is displayed on the scale and numerically with the black box above

Meters:

The LED Meters have their own scale. This time, the dB value represents an absolute value of the audio signal coming out of that component. Technically it is also a ratio, the current signal level compared to a reference level (dBu, dBV, dBFS, etc). The scale tops at 0dB, which represent 0dBFS, all bits carrying 1111... However the numerical display above can display levels above 0dB and that is where it can get confusing.

0dBFS implies a fixed number of bits (16bit, 24bit). However, in Logic this applies only to the Output Channel Strip, which represents the output channel of the connected Audio Interface, its DAC (digital/analog converter). All other Channel Strip (besides VCA Channel Strips and External MIDI Channel Strip) display Logic's internal signal level, and that is not fixed. It operates in as a so called floating point. It provides a much bigger headroom, that you cannot clip "theoretically". This is a completely different (heated) discussion. Keep in mind that ProTools (and some third-party Plugins) operate internally also in a fixed point environment, where level settings are much more critical.

Logic's attention to detail:

There are few little details in Logic regarding metering that are often overlooked. I discuss them in my book "Logic Pro X - How it Works".

For example, when you look at the meter and set your levels in a mix, you have to be fully aware of the difference between Output Channel Strips and the other Channel Strips. Logic hints at that difference. When you exceed the 0dB level on the Output Channel Strip, the top 0dB segment on the LED meter turns red and the numerical display turns also red for all levels above 0dB. On other Channel Strips, the top LED segment is "only"orange, and the numerical display above is also orange (instead of red). This tells you, "yes, you are above 0dB, but it is not that bad" (however, other people might argue that).

Just pay attention to the different color codes and how Logic displays signal levels. As you can see, every dB level in the numerical box below 0dB is displayed in a colored font, once the signal exceeds 0dB, the box itself turns color (orange or red), depending on the type of Channel Strip. More about those little details are found in in my book.

As I mentioned at the beginning, there are a lot of standards when it comes to signal levels and it is a good idea to read up about those standards and where all those standards originate from. Many are established in the analog audio era (VU, dBu) and when digital came along, new standards had to be created (dBFS) and referenced to the old standards and equipment (-18dBFS). Those topics are a little bit technical (dealing and calculating with logarithmic numbers), but many of those concepts are adapted in the modern DAWs, sometimes in different ways and "different interpretation" and that is where it can get confusing.

To finally answer your question.

• Don't exceed 0dB signal level on your Output Channel Strip (which can result in clipping/distortion)
• Don't sweat over signal levels above 0dB on your other Channel Strips (although keeping a good signal level "hygiene" might improve the overall sound of your mix)

Hope that helps

Edgar Rothermich

http://DingDingMusic.com/Manuals/

'I may receive some form of compensation, financial or otherwise, from my recommendation or link.'

Conway Tokyo wrote:

Just to clarify, 0dB on the output cannel strip is equivalant to 0dBfs. Correct?

Yes, 0dB on the Meter of the Output Channel Strip is equivalent to 0dBFS. All bits set to 1s

.

Not sure if this will help or hinder. At best it has a little history in how we arrived here (from analogue calibration to the meters in DAWs). Not specific to Logic and written for a slightly different purpose but there may be some useful info:

https://paulsmithblog.wordpress.com/2014/11/27/24-bit-recording/