Loudness in mastering – part 1(Letto 65 volte)

---

Dynamics

Dynamic range

In a piece of music or speech, it is the difference in volume between the quietest and loudest passages.

In the field of acoustic music (without amplification), the music performed by the large “Romantic” symphony orchestra has the greatest dynamic range, which can reach 60 dB.

With this type of music, the listening volume in the Auditorium can reach peak acoustic levels of around 100 dB (the most intense accents of a full orchestra, also known as “hits”).

It will be possible to distinguish even the most delicate musical passages, which could reach a minimum threshold of approximately 40 dB, provided that the volume of background noise is sufficiently below this level (there is sufficient silence in the theatre).

To ensure that most of the harmonic content is not lost in passages with very low volume, it will therefore be necessary to maintain as high a “margin” as possible between the level of these passages and the background noise threshold.

An example: 

• 35 db of ambient background noise present in an average crowded concert hall
• +    5db margin 
• +  60db at the loudest points of the music 
• = 100 db maximum listening volume at “fortissimo” peaks”

In practice, however, we need to be able to listen to recorded music at much more moderate volumes, which allow for good enjoyment even in situations where it would not be possible to exceed 60 dB above background noise, such as: listening at relaxed volumes, at night, in noisy places, in a car with the engine running, on small speakers, or as background music.

Under such conditions, listening will be more enjoyable if the natural dynamic range of music or speech is significantly reduced (for example, by half or even more), in order to make the more delicate musical passages sufficiently audible even in the above circumstances.

Therefore, bear in mind that: the lower the listening volume, the higher the background noise volume will be, and consequently the smaller the dynamic range should be, in order to ensure that every musical passage can be enjoyed without missing anything while listening.

On the other hand, reducing the dynamic range will tend to increasingly flatten dynamic expressiveness, with a reinforced “pianissimo” and muted fortissimo accents, resulting in an enjoyable but boring listening experience.

Average dynamic intensity measured

There average dynamic intensity, expressed in RMS, is the average level of the sum of the peak values detected on the timeline of a track (or fragment thereof).

Average perceived dynamic intensity

Expressed in LUFS, The’average perceived dynamic intensity also referred to simply as Loudness or even better Integrated Loudness, broadly corresponds to the average dynamic intensity measured above, but also introduces new calculation elements, including:

• a measurement based on human perceptual criteria, rather than solely electroacoustic criteria, which differ in relation to frequency and dynamic contrast speed
• an adequate decrease in sensitivity during performance breaks and in musical passages of low intensity below a certain threshold

As we shall see, the’average perceived dynamic intensity is the most recent and useful criterion for evaluating loudness of a piece of music, a particularly useful element in the field of mastering.

---

On the left is the dynamic acoustic space of the orchestra, which can express itself fully provided that the ambient noise is equal to or less than 35 dB. On the right is a comparison with the useful dynamics of a 24-bit digital recording system, equal to 144 dB, whose “weak links” in terms of dynamics are the analogue components and converters. By using high-quality equipment and paying attention to the use of levels, it is still possible to guarantee a useful dynamic range equal to that of a large symphony orchestra (60 dB maximum) even when recording with maximum peaks at very low levels (down to -30 dB). Consequently, the widespread practice of recording with peaks at -12 dB (or even -18 dB)  will fully respect the “extreme” dynamics of this orchestral ensemble.

---

Listening

Before continuing, here are some analytical examples of the most typical listening situations today:

• acoustic or amplified concerts, in theatres, with controlled acoustics and silence in the auditorium – dynamic range up to 60 dB (output power from 40 to 100 dB)
• amplified concerts with noisy auditoriums – dynamic range of approximately 25 dB (sound power level from 85 to 110 dB)
• audiovisual projections – dynamic range of approximately 20 dB (variable emission power depending on the location of use – examples: 35 to 60 dB in very quiet auditoriums, such as museums – 75 to 95 dB in auditoriums with average noise levels where a certain sound impact is required, such as cinemas – 90 to 110 dB in noisy auditoriums, such as during the public screening of a football match at a street party
• pop music listened to at home with friends – dynamic range of 15 dB – (sound power level from 75 to 90 dB)
• non-symphonic classical music listened to at home alone – dynamic range of 30 dB – (output power from 50 to 80 dB)
• music in a disco bar (sustained listening volume) – dynamic range 10 dB – (sound power level from 90 to 100 dB)
• music for dancing in a modern nightclub – dynamic range 10 dB – (sound power level from 100 to 110 dB, very tiring for the ears)
• background music – no useful dynamic range, except in flashes – as the clarity of the music will mostly be disturbed by ambient noise of varying intensity

---

Comparative representation between listening levels and ambient noise levels; the latter must be exceeded in order to ensure sufficient dynamics for full enjoyment of the sound content. Note that a margin of at least 5 dB is recommended for greater clarity of the most “delicate” sound passages. On the other hand, note the excessive volume in discos and disco bars, with margins that are too wide for sound content with very compressed dynamics: an unnecessary strain on the eardrums at very high volumes. Finally, consider the substantial “unavailability” of sound in the context of background music, whose expressive range will often be completely incorporated into the ambient background noise.

---

As can be seen, in order to ensure that the entire musical texture can be enjoyed, the dynamics will need to be compressed more and more as the level of ambient noise increases.

For background music, it will not be possible to clearly, continuously and correctly read the musical content (except for brief flashes).

N.B.

There are also cases (disco music, for example) where, due to established custom, highly compressed music at a very high level, creating very wide margins (even 15-20 dB) compared to the background noise threshold determined by the audience (however noisy it may be), which would allow us to lower the level by at least 10-15 dB, greatly relieving the strain on our ears.

Natural dynamics

We have said that a musical performance is expressed within a dynamic-expressive range which extends from a minimum sound emission level to the maximum peak produced during moments of “fortissimo”.

The difference in volume expressed in decibels (dB) between the two extremes mentioned above is defined as the “dynamic range” of the piece or simply “dynamics”.

During audio recording, the performance imprints a “track” (magnetic or digital) onto a medium.

For practical reasons, in the pursuit of optimisation as well as a standard, we always try to match the highest peak of an execution with the point of maximum undistorted dynamic range granted by the medium itself (in our case, the audio file), avoiding exceeding this limit in order to prevent distortion of the original sound wave (It's just like filling a bucket to the brim without spilling a single drop.).

In digital systems, the clipping point corresponding to a level of 0 dB on the digital scale (which corresponds to the last LED at the top lighting up red) is considered the “limit”.

This limit must not be exceeded, and it would be better if it were not even reached, allowing for an appropriate margin of tolerance, which should be between 0.2 db and 2 db, depending on the case. It is generally set at 1 db in streaming, while it is more often set at 0.3 db in mastering for CD production.

As we shall see, accurate measurement of True Peak will enable you to choose the most appropriate tolerance margin.

As we have considered, some acoustic performances use a dynamic space even higher than 60 dB, which can be considered to be approximately 90 decibels if you include moments of absolute silence, which are also part of the expressive range of the piece (basically, this means using the entire dynamic range offered by a top-quality professional analogue recorder or a 16-bit digital system, which is the main finalisation standard  commercial use of music audio files).

The above can be heard, for example, in certain passages performed by a large symphony orchestra: from the flute solo in pianissimo to the fortissimo accents of the entire orchestra, passing through pauses and moments of almost complete silence.

To ensure that the entire dynamic range can be heard, the volume should be set so that, at its peak, it exceeds the ambient background noise by at least 60 dB, in order to be able to perceive the pianissimo passages at least slightly above the ambient noise level.

It is clear that this will only be possible in very quiet environments, such as a theatre during a concert, where background noise does not exceed 35 dB, allowing good audibility even during pianissimo passages (with an acoustic pressure of 40 dB) up to fortissimo points (100 dB).

A concert with such a wide dynamic range cannot be fully appreciated in environments with high ambient noise (such as a beer festival); in such environments, in order to perceive the entire dynamic range, the fortissimo register would have to be pushed well above the threshold of ear drum rupture.

Recording dynamics

This leads to the practical need, in most listening situations, both in amplified live performances and in the reproduction of recorded music, to reduce the dynamic range of sound reproductions, up to appropriate values that allow for sufficiently correct enjoyment of music in various listening circumstances. 

With a sufficiently high compression level, it will be possible to listen to music in detail even at levels slightly above the ambient noise level, which is useful for:

• avoid disturbing your neighbours
• Do not strain or damage your ears with higher peaks when listening in noisy environments.

As is obvious, certain musical genres, due to their “sound culture”, will be severely penalised by heavy compression (for example, classical music and other genres that can be defined as “purist”); others, on the other hand, could even benefit from it to a certain extent (for example, rock-pop-dance genres).

N.B.

Excessive compression, on the other hand, is not beneficial even for the most “extreme” musical genres (such as dance music), as it will tend to:

• transform the useful audio signal into something similar to white noise, to a greater or lesser extent, depending on the amount of compression applied, which is a phenomenon that is more noticeable at high frequencies (which tend to become “metallic”;
• insert increasingly audible frequency intermodulations into the sound, which interfere with the natural harmonics of the sound, creating additional harmonic beats that distort the sound and diminish the perception of the harmonic-musical blend.

To prevent the background noise and other disorders inherent in recording media (for example, the rustle of analogue tapes) the following was sought:

• to keep the maximum peak of the recording as high as possible, but below the distortion point
• Of compress the “useful dynamic space” in a relatively narrow range, capable of reproducing a dynamic range suitable for various types of use but sufficiently wide to reproduce the dynamic expressiveness of music with dignity

In subsequent years, particularly in the pop music sector, the production industry gradually reduced the dynamic range, compressing it more and more in order to increase the volume of the lowest moments of the performance dynamics, to the point of reducing the dynamic range used to just a few dB.

As we shall see, this phenomenon has accelerated significantly with the advent of digital media.

Over the course of approximately 20 years (from the 1990s to the 2010s), the need to compress music to ensure more convenient enjoyment gradually turned into a frantic race to Perceivable volume.

The aim, encouraged by producers, was to use loudness to overcome the sound impact of competing music productions, which triggered a veritable Volume War, defined precisely as “Loudness War”.

Continued in Part 2: https://alessandrofois.com/staging-a2/loudness-nel-mastering-parte-2/

---

For more information on Digital Audio Mastering