The delay is part of the way Sonos works. It's not the line in adapter. It's present in ALL Sonos devices. There is always going to be a delay on the line-in, it needs to buffer the input in order to stream it to other Sonos speakers in your home.

The only speakers where this is not present is in soundbars and the ARC input on the Amp to allow the audio and video to be in sync. When you group a speaker to the room. the second and subsequent rooms will have a delay.

If you haven’t seen a post about this delay, just do a search in this community. It comes up dozens of time a week, in various threads. 

https://en.community.sonos.com/speakers-229128/line-in-delay-6887947#:~:text=The%20delay%20is%20part%20of,lip%20synced%20with%20the%20video.

I understand why there are delay options available for the reasons stated above, however I still feel there should be an option for 0ms (or as close to that physically possible) should a user wish to make use of that feature.
It seems silly not to have that option for scenarios where one doesn’t need a delay.

Is it that difficult to implement?

I can’t speak for Sonos on this, but I can give my opinion. While there may be many who wish to incorporate analog systems into the Sonos ecosystem, Sonos is mor concerned about whole home audio. This requires speakers to speak to each other to achieve a seamless audio experience. Would it be simple to implement a setting that eliminates the line in delay? I believe it is possible if it can be done for the Amp and soundbars. Will this implementation be a wise business decision? 
I believe it would be because it could/will open a whole new market for Sonos, like DJs adding it for wireless audio at gigs.

the bigger question though is.. is Sonos ready for that  in light of the recent changes that is still causing issues for many?

For me that would be a rather large unneeded expense as I’d have had to pay for four adapters that I’ll never use.

For others that need the Ethernet option it would be even more aggravation as they would have to pay for both adapters.

So what happens when people flood the Sonos Support line because they set their line-in delay to 0 and their multi-room music system starts stuttering and dropping out due to an insufficient buffer?

It’s only possible for the soundbars/Amp due to the low latency, one-way, ad-hoc 5 GHz network made especially for surrounds and/or subs.  That connection is not robust enough to go through walls and floors with any reliability, hence the use of 2.4 GHz and a buffer for anything meant to be grouped between rooms.  Which is why the delay is still there when grouping a soundbar/Amp with another room for TV sources,

As to opening their market up to DJ’s, the only thing separating Sonos from a standalone PA system is multi-room streaming.  The OP wants the 0 length buffer for “scenarios where one doesn’t need a delay”.  So they want to use it without the multi-room function, i.e. a standalone PA system (which is what they should buy in the first place).   Horses for courses. 

A random few milliseconds of delay when browsing a web page or setting a thermostat is no big deal, but it would be a major disruption to audio play. SONOS players are time aligned within about two milliseconds. The 75ms latency gives the system some time to work around network delays while maintaining the time alignment. Sharing multiple time aligned audio streams with up to 32 players is not so easy. Eventually, competing products licensed SONOS patents, else their product was limited to servicing a very limited number of players and time alignment was spotty.

If you have two identical CD players, each playing a copy of the same disc, simultaneously start playing the two discs. By the end of the first track there will be an obvious time misalignment between the players. On the other hand a SONOS system can play all day and into the night while maintaining time alignment (within two milliseconds) between multiple players.

I’m not aware of any 3rd party alternatives to the line-in adapter.  Last time I checked there are plenty of options for USB C to 3.5mm adapters available on the market, but no 3.5mm to USB C adapters.  These adapters are not 2-way.

Theoretically, Sonos would have to go into a ‘no grouping’ mode, where the line in source can only be played on the connected room. I say theoretically as I think there would still be  stuttering issues with a speaker pair/ sub in the room as I believe those speakers are connected via 2.4 wifi and do need the buffer as well.   But even then, I don’t think people would be happy with this. 

Sonos could maybe do what they do with TV audio, play immediately in the connected room, and delayed elsewhere (still runs into issues with speaker pairs).  People don’t like that either.

The purpose of the line in was not so that users could connect it to TV/vdieo sources, or to integrate and sync with other audio systems, it was to bring in external audio sources like turntables, CD players, etc.

This is not even factoring in that wifi audio because substantially les reliable in a crowded room to the additional interference.  There have been horror stories posted here of people testing their wedding reception venue in an empty space successfully, then getting dropouts during the actual event

Indeed.

In my opinion, providing a 0ms delay option in the app would be a practical and user-friendly feature, especially for those who primarily use a single speaker, such as the Era 300. Any potential confusion or technical issues when using multiple speakers could easily be addressed with a simple pop-up explainer in the app. This guide could offer personalized recommendations and best practices based on the user's specific speaker configuration.

Introducing this feature would significantly enhance the utility of the speakers, enabling a wider range of creative use cases, all while staying true to their core purpose and functionality.

In essence, adding a 0ms delay option doesn’t need to undermine the multi-room functionality or overburden Sonos Support. It simply provides users with more flexibility to tailor their Sonos experience to their needs. Empowering users in this way aligns with Sonos’s premium branding and innovative spirit, while addressing a growing demand for low-latency solutions.

I’d love to hear Sonos’s perspective on the feasibility of such a feature and whether it could be explored in future updates.

I’d like to add another perspective that I think resonates with a significant number of Sonos users, myself included.

For many of us, the appeal of Sonos lies in its ability to enhance and complement an existing audio setup rather than completely replace it. Not everyone has the means—or the desire—to overhaul their entire analog system or speaker collection built over years of enjoyment. Often, integrating a single Sonos speaker into an established setup can provide incredible value, such as richer sound or enhanced bass, as is the case with my Era 300.

In these scenarios, a low-latency option for the line-in adapter would allow users to enjoy seamless integration with their existing equipment without the frustration of synchronization issues. This isn’t about competing with Sonos’s multi-room ecosystem; it’s about recognizing that many customers don’t use (or need) a full Sonos system to reap the benefits of its premium technology.

I’d also wager that there are many users out there in similar situations—where Sonos speakers are used to complement, rather than replace, their beloved analog or legacy setups. For these users, offering a 0ms delay option would be a thoughtful and practical addition. It would allow Sonos to cater to a broader audience while maintaining its core strengths.

Sonos has always been about flexibility and innovation, and providing a feature like this would align perfectly with that ethos.

Perhaps you just purchased the wrong product to meet your needs, ​@Rickardo? Are you within the return window? 

Or they could not offer it at all, and not have to worry about warnings, or pop-ups, or recommendations of best practices.  Guess which approach Sonos has chosen to take for going on 2 decades?

It might be more complicated than just finding one that works in the proper direction.

In most big systems they load, or have available to load, a wide variety of chip driver code, that takes a lot of storage space.

Sonos has very limited space so it is likely (nobody official has said) that they only have the code for the chip in their adapters available.

There can’t be be a 0 sec. delay option if using the analogue input on Sonos devices, because the necessary AD conversion always will cause a delay. So imho it’s more an issue of conversion as of buffering to play audio without delay on the device directly. 
The home theater device have digital inputs and no conversion is needed. 
Buffering more is an issue of wireless data transport and needed for grouping. 

Likely, the hardware path to allow direct patching between Line-In and Line-Out does not exist. A hardware redesign would be required in order to provide this zero latency path.

Yes I can agree with that logic, but suspect that conversion rate would be in the nano seconds range and not as high as 75ms?
It would be interesting to test with other speakers that do not force-impose any sort of delay to find out what sort of discrepancy there really is...

While it’s true that Sonos has chosen its current approach for decades, innovation and adaptability are what keep companies competitive in a rapidly evolving market. Simply relying on "this is how it’s always been done" as a justification for not considering user feedback is short-sighted. Customers’ needs and expectations evolve over time, and providing additional options—like a zero(as close as physically possibly)-latency mode—could significantly enhance the value and versatility of Sonos products.

Your point about not having to worry about warnings, pop-ups, or recommendations is valid in terms of simplifying development. However, avoiding additional complexity should not come at the expense of user satisfaction or product versatility. A well-designed app can balance simplicity and advanced functionality.

Sonos has stated in the past that the Line-In is one of the least used features of its products (hence relegating it to the afterthought of an adapter on recent models).  I highly doubt “product diversity” is suffering because there is a slight delay on one of the least used features. 

In short, give it up.  It ain’t happening.  Go find a product that fits your needs instead of banging your head against the wall here.

Probably least used due to it’s limited functionality in the first place 

Well I’m not one for for giving up, I like the speaker, the fact that it did sport the line in feature convinced me to make the purchase - just a shame that such a seemingly elementary feature doesn’t existing. But you’re right - I won’t be extending to additional speakers due to the limitation…

I mean who cares about the minority right?

It’s not “seemingly elementary” to anyone who understands Sonos’ core functionality and/or the very basics of networked audio streaming.  You have put forth some flowery prose on how to make the Sonos experience “seamless”, then propose a change which by its very nature makes Sonos’ core functionality anything BUT seamless.  Popups, warnings, suggestions for best practices, and the elimination of multi-room usage in order to use a feature are not “seamless” at all.  So go buy a PA system.

Who said anything about eliminating multi-room usage? I said “seemingly elementary” since I might be missing some technical / hardware limitation that I might not be aware of, thus from my perspective it seems simple to update the app to provide 0ms delay option (or as close to it as possible).
Perhaps that’s not the way it’s built and would destroy them if they try, who knows, but I’m not really getting a clear factual based answer so far to shed light on the matter...

I honestly believe it would be a great feature and don’t thing it would be as harmful as you make it out to be. You come across somewhat aggressive, not sure if said something to upset you?

As stated before, in multiple threads on this subject, you cannot use the line-in source in multiple rooms (or even a stereo pair in the same room) without the 75 ms buffer.  It is physically impossible to sync and/or error correct the stream without 75 ms of buffering.  That's the very reason the delay exists.  No buffer means no multi-room. 

And as far as being "aggressive" goes, there are multiple threads about this going back 2 decades.  In each one, it is explained in detail why the delay exists and why it's not going away.  Yet here you are, making the same silly arguments that have been put forth, and summarily dismissed, every time the subject comes up.  After a while, it gets to be pretty frustrating hearing the same ineffective lamentings over and over again.

I think you would be hard pressed to find any audio professional, or someone who knows a thing about audio, that would claim using 2 different audio systems in the same room improves the audio quality.   You certainly are not the first person to want an 0 delay option, but it’s usually because they want a PA//karaoke/DJ system, or they want to connect it to the TV instead of getting a Sonudbar or amp.  I don’t recall anyone claiming it was needed so a Sonos speaker can play the same audio as their old audio system in the same room.   You may be overestimating the ‘many of us’ here.

However, the statement that you can’t integrate your analog system, or passive speakers, into Sonos system if false.  The Port and exists for these vary reasons.  The port has an output that has no lag with the rest of the Sonos system, so your analog receiver/amp can play in sync with the rest of your Sonos gear for Sonos sources.  If the source is your analog system, then yes, you do have the delay, which isn’t a problem if your speaker systems are separated in different rooms, as would be the case for the majority of users.  If you just want to use your passive speakers without your old amp, then Sonos has an amp for to power your speakers.

That’s on you and not an excuse to be a jerk. Be an adult and ignore the thread. 

If you have a problem with my posts, feel free to ignore them, or report to the mods.  As a mod said recently, it is not up to posters to police threads.

And by the way, I don’t see me explaining multiple times why the delay exists to someone who refuses to believe the explanation as being a “jerk”.