-b 40 -m j -V 4 -B 320
is the same as:
--preset medium

and

-b 32 -m j --abr 104 -B 320 -q 0
is the same as:
--preset 104 -q 0

right?

The presets contain code tweaks that can't be emulated exactly with other commandlines and are therefore supposed to be more optimised.

I'm not optimising anything, just wondering if above commandlines give the same results.

The results might be similar but I doubt they would be the same. I remember LAME devs always telling people that no commandline really equals the presets.

They seem to be pretty identical, that would be because presets code is used even without using the --preset switch...
It looks like presets are no longer special tweaks which you can enable by the --preset switch. Now the preset's code seems to be the main LAME code, used by default, and different presets (medium, standard, extreme) work all the same way, except that they have different bounds for lowest & highest bitrates and maybe different VBR quality (and lowpassing etc.) - things that you can as well alter by the -b, -B, -V, etc. switches. They could be called profiles now. Is that right?

Bit-to-bit comparison would be required to check your statement.

Anyway, how do you know that --preset switches are no longer special tweaks?

I'm not sure. A LAME dev would be able to tell the answer, but I could swear that they still tell people to just use the presets. I could be wrong however.

At least some values of the -V parameter have been mapped to the presets starting with LAME 3.95 (evidence here).

Mp3's coming from the commandline sets in the 1st post are bit identical (the 1st set gives mp3's with 3 bytes different, but these bytes are in the header and don't affect audio data).
And I didn't mean that the presets are no longer special, I just meant that you don't need any special switches to activate them - they seem to be used by default, like they were the main LAME code now.
A couple of versions ago you could ask for switches which emulate presets, now we can talk about presets which emulate switches

My mistake. I guess I'm still living in 3.90.3 land.

No. This is the same as:
--preset medium -b 40



yes.


New Lame versions are ALWAYS using presets. Examples:
-b128 == --preset cbr 128
--abr 128 == --preset 128
-V4 == --preset medium
-V4 --vbr-new == --preset fast medium

Hmm, why -b 40? Isn't medium preset bound to the lowest bitrate of 40kbps by default? (except when there's a digital silence so it uses 32kbps)

no

What is the default lower bound of bitrate for medium preset then?

There is no, so it is 32kbps (the lowest possible)

To make things ultimately clear for me, are you absolutely sure that "-b 40 -m j -V 4 -B 320" isn't the same as "--preset medium"? If I understand switches correctly, "-b 40 -m j -V 4 -B 320" allows use of 32kbps (on digital silence), "-b 40 -m j -V 4 -B 320 -F" doesn't, so if there's no -F switch, then it should be the same as "--preset medium" ...unless "--preset medium" = "-b 32 -m j -V 4 -B 320".

I am sure.

--preset standard is, AFAIK, the only preset that uses code-level tweaks and is therefore not equivalent to any command line.

Could someone clear up what type of code tweaks preset standard/extreme/insane are using?

In current Lame versions (right now 3.96.1), presets are always used.
So this "unreproductible code level tweaks" thing is something from the past:

--preset extreme == -V0
--preset standard == -V2
--preset medium == -V4