In which gain staging and VU meters make me cry

[Aled Hughes]

I've changed my channel meters in Reaper to show LUFS-M, but unfortunately they default back to peak meters if a track is record enabled.

I find peak meters next to useless - a numerical display showing the max peak level above the meter is plenty (or a light perhaps)

The Reaper master meter is very configurable, and I've got that at LUFS-M also, with a -20dBFS sine wave reading '0' at the moment. The meters turns yellow above 0 until +10, at which point it turns red. There is a numerical peak display above it, and a numerical LUFS-I display underneath. I aim for my mixes to hover around the 0 mark, or just below. I find this works well.

I'd really like the channel faders to be this configurable, but in the meantime I've set up the included JS loudness metering plugin with it's embeddable GUI as a sort of traffic light system when setting input gains and mixing - I haven't quite settled on it yet, but at the moment it turns yellow at -30 LUFS-M, and red at -24 LUFS-M. When setting up initial gains when tracking or getting a rough balance in a mix, I try to aim for that 6dB yellow window. This seems to give me a mix at around the master fader's '0' as stated above. Really, it's a continuation on the 'pink noise mixing' approach to set initial levels.

I've recently set up this system, but it seems handy to me, although I might bring the target levels down somewhat for tracking as the peak levels were sometimes higher than I'd like. It's a work in progress...!

[Hugh Robjohns]

I've changed my channel meters in Reaper to show LUFS-M, but unfortunately they default back to peak meters if a track is record enabled.

I don't think that's unreasonable.

When tracking the peak level is the single most critical parameter, since converter clipping is unacceptable. However, when mixing you don't need to know the peak level -- it's already a safe value -- while the instantaneous loudness of the track is a critical factor in the mix... and the Momentary Loudness value indicates that quite well (it's actually very similar to a proper VU display!)

[Mixedup]

I wish that you could turn off the meters in Logic, so you don’t see them

Yes! This is a feature all DAWs should offer!

[tomdot]

If we’re going further, I think there should be a sample of Geoff Emerick tutting whenever your signals go above a specified threshold.

[Aled Hughes]

I've changed my channel meters in Reaper to show LUFS-M, but unfortunately they default back to peak meters if a track is record enabled.

I don't think that's unreasonable.

When tracking the peak level is the single most critical parameter, since converter clipping is unacceptable. However, when mixing you don't need to know the peak level -- it's already a safe value -- while the instantaneous loudness of the track is a critical factor in the mix... and the Momentary Loudness value indicates that quite well (it's actually very similar to a proper VU display!)

Certainly not unreasonable, but it would be nice to have the option now that they’ve incorporated it when tracks are not record enabled. I just don’t need that much screen space telling me how far I am from clipping!

[Richard Schiller]

Apologies for being a bit late to this discussion. Maybe some of this might be useful to someone reading this thread:

Metering operational sound levels is a complex topic and no one should feel bad for finding it so. Meters are needed for two very different reasons, to balance sound and to prevent over modulation. Originally, it was the over modulation of transmitters and then magnetic tape but now it is the finite capacity of digital coding that needs to be addressed.

The BBC peak programme meter is not, as is widely thought, a peak meter but instead a compromise to indicate programme level yet give some idea regarding over modulation. It's a clever piece of UI design. The way to ensure quality across a huge organisation with many different users was to standardise. In level terms, this meant lining-up every piece of equipment for zero gain and with similar headroom. In the analogue era this was solved by distributing reference level tone and aligning to that. Line-up level was defined as BBC PPM 4. This was vertical for the meter needle - both easy to remember and easy to read.

By the way, BBC PPMs used needles that swept an arc for a reason. The human eye is most critical when viewing angular displacement - we have to be good at this as we use it as part of our balance system.

When reading programme levels, the meter was designed such that typical speech would average around PPM 4. If the needle seemed to be as much above 4 as below, then your programme would sound similarly loud to another balanced in the same way. Controlling the music of the day to also average around PPM 4 worked too. Later music would be more compressed and anyway, with all sounds, the operator had to use their judgement to create the sound field required for the programme. In summary, '4' was both the target for line-up tone and the target for balanced content. More experienced operators knowing that this nominal level would be varied with specific content types.

The BBC PPM was not perfect and peaks would get through but only short ones and compressors and peak limiters mounted at the end of the chain would ensure they were taken care of. Remember, clipping just a short peak does not matter to the same degree as clipping the body of the sound would. When recording, the magnetic tape recorders would naturally provide compression of the occasional short peak.

BBC PPM meters were very costly. The later VU was introduced as a more affordable meter but was also designed for a different purpose. As the name implies, it is there to match volume (how loud the programme is) not indicate peak levels at all. As a volume indicator, the VU meter is sometimes superior to the BBC PPM. As a peak indicator, it is always worse. The ever-present comparison between PPM and VU is somewhat unfair - like comparing a measuring jug and a kitchen scale.

The VU meter's biggest drawback for programme level indication is that it is not linearly logarithmic. The BBC PPM had 20 and then 24dB of dynamic range of true logarithmic indication - plenty enough for the purpose for which it was made. The difference that being linearly logarithmic makes, in practice, is that it allows the operator to mix to different levels. You can mix some louder voices and then say a quieter conspiratorial whisper, hitting two different spots on the meter.

On a purely aesthetic level, this is what makes choosing between VU and PPM meters rather difficult. The ballistics of the VU are arguably more pleasing but only when the audio level is exactly at the sweet spot. For general use, the PPM therefore looks better.

In the digital domain, we don't have the luxury of tape compression or (at least usually) analogue delay line compressors and limiters and so the requirements for digital metering are different.

In digital, true peak meters have become common though not because they address its unique challenges but rather because they are easier to code. These have an instant rise time and so indicate absolutely any overload peaks. This instant response would seem like a good thing and in some ways it is. However, clipping very short peaks is less important than clipping the body of the sound and such meters do not discriminate. Remember, if you have silence with just a single sample peak and it is clipped, then programatically there is no distortion.

Some of these peak-reading meters have been given a slow fall-back like the BBC PPM. On the one hand, a peak reading has to be held or else you won't see it but on the other these ballistics suggest a programme capability which such meters don't have. A meter with an instant rise time and slow fall back is not a programme meter and so is not a PPM - though invariably that's how they're labelled.

As has already been suggested, when recording you will be more concerned by over modulation. When mixing, it is the programme level (getting the volume right) that matters most. In the analogue domain, the BBC PPM did a fair job of both. The VU was definitely a mix meter rather than a recording meter but was of course used for both anyway. Neither though are designed for the wide dynamic range we now have thanks to transistor pre-amplifiers and cheap high-performance analogue to digital conversion.

Many years ago I patented a programme meter for digital operations. It had two indicators, one for programme level and another for over modulation. I still think that this is the only way to solve the dichotomy. The level indicator was a bit like a linearly logarithmic VU meter but improved to be linked to audible volume (using a weighting curve to match the ears response). It was the foundation of later Loudness Unit measurement. The over modulation indicator was something like a peak meter. So as to not be distracting, it would only display when sample levels got near maximum and would gracefully fade away when not needed.

[Hugh Robjohns]

Apologies for being a bit late to this discussion. Maybe some of this might be useful to someone reading this thread:

A useful contribution indeed -- and thanks for that -- but there are a couple of points I'd like to pick up on to avoid potential confusion in other readers.

Meters are needed for two very different reasons, to balance sound and to prevent over modulation.

I'd say three key reasons. The first, and arguably the most important, is for equipment alignment. Meters allow us to optimise the reference signal level between the noise floor and clipping level, as it passes through different pieces of equipment in the signal chain, as well as to ensure unity gain throughout the signal path.

The second is to warn of over-modulation -- although that is much less critical now than back in the day as we generally work with more headroom now -- and the third is as an aid to mixing and maintaining consistent perceived loudness levels, as you say.

The BBC peak programme meter...

The analogue PPM was/is not exclusive to the BBC. Pretty much all European and Scandinavian broadcasters developed very similar PPM designs around the same time using the same core technologies.

The BBC's PPM has a unique simplistic scale (officially known as the type IIa PPM), but the underlying design and response is is also used in the otherwise identical European type IIb PPM, and is functionally very similar to Type I PPMs often known as the DIN meter, (and the Nordic meter is a variation of ot, too).

When reading programme levels, the meter was designed such that typical speech would average around PPM 4.

You won't find many networks that keep speech averaging around PPM4 today! Most tend to keep speech in the top half of the meter, around PPM5 or (if more compressed) PPM6.

The BBC PPM was not perfect and peaks would get through but only short ones and compressors and peak limiters mounted at the end of the chain would ensure they were taken care of.

This was an intentional element of the original design and was introduced specifically to avoid operators under-modulating the transmission networks. Occasional brief transient overloads were deemed acceptable (and generally unnoticeable), and a higher overall modulation level was more desirable. The Type 1 and Type2 PPMs really only differ slightly in the duration of transient peaks they ignore.

Remember, clipping just a short peak does not matter to the same degree as clipping the body of the sound would.

This is true for the analogue world, and that's why PPMs evolved the way they did, but brief peak clipping sounds considerably more obvious and intrusive in the digital environment than in the analogue one (mainly because it creates aliasing which results in unnatural anharmonic distortion).

BBC PPM meters were very costly. The later VU...

Not much later! The type 1 (DIN) PPM was defined in 1936 and the type II (BBC) PPM in 1938. The SVI (better known as the VU) was defined in 1939, but the work to develop it was a couple of years earlier...

That said, the PPM's conceptual origins can be traced back to the late 1920s in the telephone industry, and the BBC's development of those concepts into the 'Smith' meter in 1932.

The ever-present comparison between PPM and VU is somewhat unfair - like comparing a measuring jug and a kitchen scale.

We can certainly agree on that!

The ballistics of the VU are arguably more pleasing but only when the audio level is exactly at the sweet spot.

Yes, the criticality of correct VU calibration is overlooked by many.

In digital, true peak meters have become common though not because they address its unique challenges but rather because they are easier to code.

The term 'true peak meter' has acquired a significant and specific meaning that is different to the one I think you are describing here which is more accurately referred to as a 'sample peak meter'.

Most digital recorders and DAWs simply examine short blocks of digital samples to ascertain the loudest sample value, ad then display that on the meter -- hence 'sample peak meter'. It's very simple and fast to achieve, through both hardware and software implementations.

However, while an entirely acceptable solution for most purposes, it is not accurate when it comes to evaluating the actual peak audio levels as reconstructed from the digital data.

For example, most sample peak meters will indicate an overload ('over') if a single sample hits the top quantisation level (0dBFS) -- and yet this can be a perfectly legitimate situation which does not represent an overload at all. To overcome that issue, some early digital meters only warned of overload when a number of consecutive samples were at 0dBFS (Sony settled on four consecutive samples)... but again, this could be perfectly legitimate non-overload condition for a low frequency signal.

So sample peaks meters often warn of overloads that don't actually exist, and at least that's erring on the side of safety... However, they can also fail to warn of overloads that really do exist -- known as 'inter-sample peaks' and that's a much more serious problem when working intentionally close to the clipping level (as CD mastering stupidly did/does). These inter-sample peaks occur frequently in peak-normalised music as the reconstruct analogue waveform often peaks significantly higher (3-6dB) than the peak level of individual samples, resulting in an overload of the D-A circuitry.

For this reason, the BS1770 loudness metering system includes an oversampling peak metering element specifically to detect inter-sample peaks, and this is defined as the True Peak Meter. So it is important now to be clear in the use of the terms sample peak and true peak meters in the appropriate contexts.

Remember, if you have silence with just a single sample peak and it is clipped, then programatically there is no distortion.

In the digital realm clipping distortion results in aliasing which is much more obvious and unpleasant to the ear than analogue transient distortion, hence the far more stringent metering requirements to avoid digital clipping.