Here are two statements that paraphrase views about jazz recordings I've heard quite a lot over the years;
1) I just listen a lot more to the older jazz records - I like the sound of them
2) ECM records have too much reverb
These opinions make me think about fidelity. Fidelityis a measure of how closely the recorded (and transmitted) sound represents the sound of the source in the environment it was recorded. It is possible to record a solo piano or a voice in hi-fidelity with a handful of mics in a good-sounding room. If you have a whole band playing, you face a conundrum; does a combination of the highest-possible fidelity representation of all of those instruments individually produce a truthful account of what they sound like, together? The answer is probably no. In order to create a believable space in the recording, engineers build an artificial 'room sound' for the musicians in the mixing process using reverb, stereo placement and eq, and/or record all in one room in the first place and try and capture the sound of the band in the room as well as the sound of each instrument. It all sounds a bit nerdy, but the more records you listen to the more you start to realise how profoundly these decisions can affect the connection between the artist and the listener.
The sound of most of German record label ECM's recordings is concerned foremost with fidelity to the full timbres of the instruments, which are all clearly heard, beautifully-recorded and balanced. I have to say that I love the sound of most ECM records, and usually find that the music being made on them seems to organise itself in the knowledge that it's going to end up in that sound-world. Spacious, sensual, open...the detail in every moment is crucial. The statement 'ECM records have too much reverb" is a statement about lack of another kind of fidelity - fidelity to the sound of a gig.
From this perspective you could argue that Coltrane's Sound is a higher-fidelity recording than, for instance, All Our Reasons, Billy Hart's 2012 recording for ECM. Same lineup, and for me some similar musical processes going on. There are some very noticeable differences in sound, though:
The bass is a lot fuller and rounder in the 60-100hz range in the modern recording, as you would expect. I checked out the eq curves over short samples from, both 'Liberia' from Coltrane's Sound and Tolli's Dance from All Our Reasons. The Coltrane is a lot more present in the upper mids, and oddly enough has quite a lot of almost sub-audible bass. There's a bit more high end (above 8khz) sheen on the Billy Hart record. When you listen to a gig, particularly in a small jazz club where bassists are modestly amplified and there isn't a large PA, you don't hear a great deal of low end sub 100hz because it just isn't being generated. Likewise much of the very high end is being absorbed by people and all their soft bits (beards, threadbare wooly jumpers, Kangol caps etc. etc.)
Each instrument is placed in one distinct place in the stereo field in the Coltrane recording. In All Our Reasons the piano and drums are very much in stereo, both giving us lots of information across the whole spread. It's a very 'enveloping' kind of sound. (N.B. every track on Coltrane's Sound features a different stereo setup. It's quite strange when you notice it - it's like everyone's wandering around in-between takes like a fielding side in a game of cricket!)
3) The sound of the individual instruments
For a driving, swinging track there isn't a lot of ride cymbal in the mix in Liberia. In fact, there's not all that much drum 'information' - they're quite back in the mix and restricted to the midrange. Often the drums were physically stationed far away in the recording room during this era, to reduce presence and spill into the other mics. The piano doesn't show much bass or high-end (both features of the ECM record), and is basically in mono. Now of course all players actually sound different - but Coltrane is definitely 'at the front' here compared to Mark Turner.
Fairly obvious - the ECM recording has quite a lot of added reverb, which runs right down into the lower registers. The ambience in Coltrane's Sound comes from the room that the band is playing in. You can really feel it, especially if you listen to the drums.
Modern recording and mixing techniques are often focussed on bringing out detail and making every individual instrument sound as full and faithful and natural as possible, even in a busy performance. So why do we keep coming back to the sound of older, less 'good' recordings? Some people say it's all about the gear - the old desks, the tape machines, the valves.....I think a large part of it is also that there's a more space for the real sound and feel of the group to come across when there's less detail in the foreground and the listening experience is much closer to being at a gig. Coltrane's Sound is a very natural-sounding place to me because, just as when I go to a gig in a small jazz venue, the instruments are in quite distinct places, the piano is a bit tinny, the drums are at the back of the stage and you can't always hear what the bassist in playing! (Actually you can on this particular recording, though on many Coltrane records the bassist has a tougher time in the mix....) Every instrument, apart from the sax, is quite heavily compromised in terms of fidelity, but in that sense the listening experience is actually quite faithful to the feeling of being at a gig. The detail in the band (and particularly in the drums) is there, but you have to listen for it a bit harder.
I sometimes feel like having a less detailed sound actually allows the natural groove and spaciousness through on the recording, making the emotional connection to the music a little easier to establish. Some music benefits from the more detailed, lush, assembly treatment, and I that's why I disagree with people that say that ECM records have too much reverb. For other music, though (particularly very heavily rhythmic or groove-driven ensemble music) that sound can just contain too much information!