What is compression?

As it applies to audio, DNR stands for Dynamic Noise Reduction and is a registered trademark of National Semiconductor (now owned by Texas Instruments). DNR became popular in the 1980s as a way to reduce hiss and background noise on cassette tapes and AM/FM radio without needing any special encoding -- GM featured it in their Delco car radios from the mid-'80s through early 2000s, and several models of processors were sold to add it to your home stereo system.

Here's a web page which tells you more than you ever wanted to know about DNR and how it compares to other noise reduction systems like Dolby B/C and dbx:

Dynamic Noise Reduction and the DNR System 911 Overview

 

Limiter is not compressor.
Peaks limiting and DR compression are quite different procedures.
Also when a compressor is abused to the degree to “brick-wall” levels, it loses its compressor quality.

It’s not compression, but simply a serious non-linear distortion. To categorically avoid in pro tape recordings.

I couldn’t understand what you mean by “good reason”.

Right.

In my opinion, compression does not “normalize” peaks.
It’s the normalization procedure in sound processors that does.
Different tools.

What do you mean by “poor dynamic range”? For some vocalists, a 20 dB DR is quite good, and for a scene in an opera house with orchestra, soloists and choir playing and singing forte-fortissimo simultaneously, with their natural DR of about 120 dB, reducing it to, say, 20 dB DR makes it simply waste.

Who and where, except for big opera houses and concert halls, can listen to an “original sound” like, for examples, scenes in an opera house with orchestra, soloists and choir playing and singing forte-fortissimo simultaneously, with their natural DR of about 120 dB?

Very probable for some cases.

 

From the Handbook for Sound Engineers, 1987, first edition, which is one of my standard texts on my shelf: "A limiter is a compressor with a high compression ration, usually 10:1 or higher."

From Sound on Sound: "Limiter — An automatic gain-control device used to restrict the dynamic range of an audio signal. A Limiter is a form of compressor optimised to control brief, high level transients with a ratio greater than 10:1."

 

Very well, it can “compress” a DR to “30:1”, “50:1” and “100:1”. Then, by the author cited himself, it’s a LIMITER.

Right. Then, by the author cited himself, it’s a LIMITER. Where’s a contradiction with my post?

 

You said, "Limiter is not a compressor," your words. The Handbook says "A limiter is a compressor" Those are contradictory statements.

 

Diagrams to see compressor-limiter DR treatment difference:
http://www.filedropper.com/comprlimiterdifference

 

You said compression and limiting are "quite different procedure". Yet they can be accomplished by slightly different settings on the same device.

 

Compression is 'gain below a pre-determined threshold' for instance a 4:1 compression ratio means that the 4db you put in results in a 1db increase in output and so on.
So, you can now increase the overall volume. Some skill is required in adjusting the timing controls (attack and release) so that the result doesn't pump or 'breathe'

Limiting as mentioned in posts above involve higher ratios with fast attack and release times,to limit the peak amplitude, a gunshot for instance,and to stop it from distorting as it goes into the 'red'
Creative use of compression and limiting can yield interesting effects.

PCM audio becomes horribly non linear above 0db full scale, but this doesn't stop people from using only the last 15db or so of a system that is capable of 90db dynamic range.

As they say 'up is louder'

 

A limiter is a type or subset of a compressor, always has been, always will be.

 

No.
Please see the levels compression and limiting diagrams I posted above.

4:1 compression ratio means that, for example, a “minus 40 dB” signal you put in becomes “minus 10 dB” signal, that means “30 dB” increase in output.

A “minus 20 dB” signal you put in becomes “minus 5 dB” signal, that means “15 dB” increase in output.

A “minus 10 dB” signal you put in becomes “minus 2,5 dB” signal, that means “7,5 dB” increase in output.

So, a “minus 4 dB” signal you put in becomes “minus 1 dB” signal, that means “3 dB” increase in output, not “1 dB increase in output”.

 

But don't forget there is also a Knee (often very soft) and a Threshold (compression only begins when level gets this high), not to mention the Attack and Release controls, so it's not like a 4:1 Ratio means you are ALWAYS slamming the entire audio into a quarter of its original range.

When I'm mastering, I never go above about 1.5dB of Gain Reduction on the compressors, medium Attack and Release settings, low Ratio, very soft Knee, Threshold set so only the very loudest bits get "ridden", HPF in the side chain set so that the low end doesn't trigger any compression etc. I'm compressing tastefully most days for most of the last decade.

 

A compressor has a ratio above a particular threshold where compression kicks in, such as 4:1 or 10:1. An increase in the volume will always mean an increase in the output, there is no maximum output signal level, although it can manage the level.

A limiter is more to prevent the signal from going above a certain level, such as 0dB on a CD or above peak modulation on vinyl. This can mean increasing ratios as the signal approaches a maximum level which it should not cross.

Both can utilize an "attack" and a "release" envelope to make the otherwise instantaneous volume reduction and subsequent return more musical, although a limiter must not have a slow attack that will let transients through if it is specifically there to prevent their damaging effects.

 

I really don't understand why in 2021 CDs are still consistently more compressed than the vinyl. What’s the point?
One more reason to listen to vinyl.

 

Not true.
Compression is added during the recording and mastering process, nothing to do with the play-back medium

 

Not according to Album list - Dynamic Range Database

 

The "glass ceiling" analogy works for me.

This is the kind of thread topic I enjoy the most. We used to have these discussions all the time here. What happened?

 

I believe you are mistaken. A limiter is indeed specialized compressor. It works only on peaks at a threshold you set.

Tape saturation is/was often used in pro audio recording to attain a certain sound quality. Not all engineers are such sticklers to a rule.

 

It's generally advisable to master differently for different media. The noise floor of vinyl is higher, the supportable range lower. A final master for vinyl could be supported on a CD but it would waste the benefits of the medium. A final master for CD should be unsupportable on vinyl. A compact disc can handle a much broader range then, but the reason that excessive compression tends to happen on digital masters destined for CD and download sales is because digital rips are usually listened to with compromised dynamic range - when listening to music while competing against loud environmental sounds - in cars, on subways, walking around in cities, etc. This is why the quieter parts of music tend to be boosted - so the listener can hear it over the babble coming from outside their ****ty in-ear headphones.

The reality is that compromised-environment mastering should be another final master of its own, entirely separate from home audio digital and vinyl masters. The reason this doesn't happen is both overhead and demand. For years, the record industry fobbed us off with CDs that were straight transfers or primitive single process filters of original vinyl masters - even though market demand was there for remastering fairly quickly, the demand on the engineers capable of remastering meant that only a tiny subset of recordings could be addressed at any given time.

For popular music - pop, rock, rap, country, etc - the bulk of consumers of digital audio want high compression so that they can hear the song over the environment that they do their listening in. The perverse outcome is that you may find more dynamic recordings on vinyl among these genres today. Or you can switch to listening to classical and jazz recordings, which don't suffer as much from the market forces of iPhone listeners.

 

But rarely done.

 

Not really sure it's advisable. There are so many playback systems and a plethora of media out there, you can't account for all of them. I generally don't make more than one master unless asked to by the client. My digital master will be dynamic, and able to be cut to vinyl or burned to CD or cassette. I take the genre into consideration far more than the eventual playback medium (which is usually digital files and streaming these days), in trying to achieve a good sounding result. This generally translates well to most systems. But I'm also not one for crushing things, unless requested (not so often, thankfully).

 

The Dynamic Range score is meaningless on analog formats due to waveform tilt creating spurious transients. This was proven by an engineer who was surprised to see that the vinyl release of an album he worked on had a higher DR score than the CD version, even though he knows for a fact that they both came from the same master and thus have the same dynamic range.

This is because while a CD is capable of perfectly reproducing a square wave down to DC (0 Hz), a vinyl record groove cannot. If you try to reproduce a square wave on vinyl, both the cutting head and playback stylus will overshoot, creating fake transients that will falsely increase its measured dynamic range, even though they are just spurious distortion.

In fact, you don't even need to cut a vinyl record to see this happen. Dub a copy of a CD via the "analog hole" and compare it to a direct digital rip of the CD, and unless both your CD player and recording device have perfectly flat response down to 0 Hz, you'll often see that the analog copy appears to have greater dynamic range than the ripped copy.

 

Mostly true! Loudness means the average will be high, peak levels clamped to within a few dB of the average level. But loudness is also the result of increased bandwidth and also the density of the mix. Even some dynamic recordings can sound louder than others, because of their effective bandwidth. The wider the bandwidth, the louder the perceived sound (and in reality more air molecules set into motion via modulation) A recording of 80Hz to 10kHz could be compressed to oblivion, but the same recording with a wider bandwidth of 35Hz to 16kHz will sound more substantial and "powerful". Most music and sounds, voice, contains nulls. When these nulls are filled by other instruments, the holes are filled with something! This increases the density of the mix. Music becomes louder by filling these "voids" and also by layering of more instruments and vocal parts! When overdone, the music turns into mush!

As mentioned by @guestuser an increase in distortion also increases the overall loudness and energy of the music, its density and bandwidth! Harmonic distortion adds harmonics to the music that was not there!

 

They do. For example, Sony's is called AVLS: Automatic Volume Limiting System. When you engage it, it limits the max volume, and you can compress it more by increasing volume with volume dial, so quite parts will get louder, but loud parts will get limited. Useful on a bus or in subway

 

^ quiet, not quite.