This is a term that I often hear in headphone reviews here. But I confess that I don’t really understand what it means.
In loudspeakers, compression refers to the reduction in a driver’s efficiency as its voice coil heats up…
I don’t think this is how it’s being used in headphone reviews though. So maybe someone could explain what it refers to in this other context.
It depends on the context. Offhand, I can think of several meanings:
There may be more too.
It’s usually used to refer to 4.
A loss of differentiation of loudness.
Picking on a couple of headphones I’d describe what I hear as compression
I find the treble in the 1266 sounds compressed, cymbals lack in the way they decay.
Some of the older Dan Clark headphones sounded compressed if you didn’t get the volume level high enough (way too high for my personal tastes).
Not saying either headphone is bad, people love them.
I’m not sure either case is actual compression in the studio effect sense of the word, but the effect is similar.
As far as I can tell it usually describes a subjective sense of the music feeling like the contrast between loud and quiet is compromised. I know with Resolve for example, it often comes about to describe the sensation he hears when low treble resonances causes percussion to sound homogenously forward.
It would probably need to be unpacked on a “by-reviewer” basis to get to the truth since I think we all use the word a bit differently (at least in terms of which areas of the FR may cause that impression), but I think in general it describes the perceived loss of dynamic contrast (regardless of if this is actually what is happening, electroacoustically).
Thank you generic, Polygonhell, and listener for each of your replies. This helps me understand it a little better. I’d be interested in hearing @Resolve’s take on this as well, so I feel a bit less in the dark when terms like this come up. Because I’d really like to know what this is about. 
There are two other types of compression that I’m used to hearing about and discussing in audio circles btw. Data/storage compression, used to condense audio content or recordings into smaller files. And dynamic range compression (DRC), often used to increase a recording’s loudness. (I sometimes refer to this as loudness compression or just a compressed sound).
Both of these are properties of audio recordings, and not transducers. Though they can certainly affect the quality of the sound that you get from a pair or headphones or loudspeakers.
From your comments above though, it sounds to me like some reviewers here may be trying to apply the concept of DRC to describe what they’re hearing in a headphone’s FR, which is a little confusing.
File compression doesn’t apply to headphones, and it is mainly discussed in audio regarding degraded sound quality.
There are different ways to compress the dynamic range with recordings. This is a routine consideration with music production (e.g., electric guitars), as some instruments are overpowered by others.
Perceptually, I hear dynamic range compression when using the Sennheiser HD 600 versus my Focal Clear. I’ve not measured it, but it seems to follow from the construction of the driver (e.g., plastic on the Sen). This may be part of the reason why the HD 800 family changed to larger drivers.
There used to be weapons to battle the dreaded forces of compression.
Don’t think dbx makes these sorts of things any longer. 
Maybe the Schiit guys could do a modern re-interpretation of it.
They are properties of everything.
Yes engineers will deliberately add compression to elements on tracks using a compressor, and it’s commonly needed to make a recording sound good. But anything that is artificially reducing dynamic range is causing compression. none linearity in amplifier gain can cause this, it’s fundamentally what a compressor is, it’s just that but intentionally.
The most obvious mechanism for it in a transducer is none linearity of stiffness in the surround.
In speakers and to a lesser extent headphones there is usually some minimum volume level where the transducers seem to come alive, and I’d always attributed it to this effect.
Regarding Dynamic Range Expanders, not sure they are needed with digital audio. Still may relavent with vinyl.
Dynamic range compression was often used in the heyday of AM radio as it tended to increase the effective coverage of the radio signal.
I always took compression to mean that the sound gets congested during loud passages, losing clarity and some degree of noticable distortion. With highly resolving headphone setups, with older recordings, one can actually hear the effects of this from the recording itself.
Absolutely, SSN757!! And I appreciate all the continuing input and replies on this.
You can hear DRC in many new recordings as well. Most popular music is still compressed or limited in dynamic range to make the recordings louder and “better sounding” on gear where the volume or dynamic range is more limited. And in many cases it also results in audible distortion.
Haven’t experimented with them at all, but I believe there is software that can do this with digital audio.
Makes sense.
Compression is a reduction in the dynamic range between the quietest and loudest passages in music or any audio sample. There are many reasons and methods for introducing compression and expanding the compressed content back to original.
The RIAA curve reduces bass to cause a reduction in the amount space required to press a track (groove) in an analog vinyl recording. It is also used to reverse the process on playback.
Reducing the amplitude of the change from quiet to loud permitted an AM radio to transmit a louder average signal. A side effect is distorted S sound and popping from breath release on certain consonants.
You may also notice fatigue or congestion, particularly in symphonic music or other forms that typically have a wide dynamic range in music that was compressed and not corrected.
Notoriously radio and television commercials may use compression to sound louder than other content. While regulations may ban increasing absolute volume, compression gets around this by increasing average volume. Listen to the sound and you frequently hear artifacts with sibilants and breath release.
Right.
Interesting. I listened to alot of AM in my yout’. Mostly WLS in Chicago.
I still have a little trouble with the concept of congestion as well. Perhaps that would be a good topic for another discussion. I understand that alot of this is subjective though.
When I’m congested, I seem to hear lower frequency sounds better than higher frequencies. But I doubt that’s what people here mean when they describe a headphone as sounding congested.
Not 1000 WCFL? I recall many of the 50,000 watt clear channel stations.
1030 WBZ. Boston
1020 KDKA. Pittsburgh
1120 KMOX St. Louis
1060 KYW. Philadelphia
1010 WINS. New York
1090 WBAL Baltimore
I probably wasn’t close enough to get a good signal from most of those on the transistor and car radios I used.
The dbx devices were developed in the 70s and were certainly intended for use with the LPs (and cassette tapes) of the day. But the “Loudness Wars” were the worst in the mid-1990s to early 2000s, well after the advent of digital audio.
The compression of the Loudness Wars was due to production and mastering decisions, not technology limitations.
I retracted my previous remark on this because I think it might have been confusing.
This is what a phono preamp is for. However, RIAA equalization would probably not be the best example of dynamic range compression in my book, because this type of equalization really affects the spectral balance of a recording as a shown below.
There is a difference between altering a recording’s spectral or tonal balance, and it’s dynamic range. One changes the relationship of the high vs. low frequencies (and sometimes also the midrange frequencies), as indicated on the graph above. While the other changes the relationship between the louder and quieter parts of the recording, as has previously been stated.
Don’t forget CKLW in Windsor, Ontario.
Yep. Those were some lousy sounding recordings. Many of the Jazz recordings from the 50’s/60s actually sound better than the ones made during the loudness wars.
