Why is there input delay on line-in and digital inputs?

I tend to use specialized for purpose tools for each task, audio and otherwise. For me there are much better approaches to sound reinforcement than attempting to paste a microphone and a couple instruments on to a home audio system. Many years ago (before SONOS existed) I attempted this and quickly became bored because the results were not very good. I suppose that part of my issue, was and still is, that I’ve used professional sound reinforcement equipment and there is a world of difference in the results. By the way I would not enjoy using pro sound reinforcement speakers for home audio listening -- these speakers are designed for large areas and sound awful in a small room. Currently, there are compact, reasonably priced mixer/processors that can be used at home for your instruments, feeding into a basic power amplifier or powered speakers. What had required a whole rack of boxes and thousands of dollars, can now be done in a compact box for a few hundred dollars.

There is also a generational bias to this discussion. More and more the younger attitude is “isn’t everything wireless now -- Bluetooth or Airplay?”, but older folk chafe at this. And technology is constantly evolving. Techniques that were impossible, impractical, or enormously expensive only a few years ago are now cheap and trivial. An example is the $10 Bluetooth speaker I saw hanging on a peg at a clothing store checkout. I’m not suggesting that this would be a great sounding or preforming product, but ten years ago you’d be laughed off a design team for even suggesting this sort of product.

Martech,

I’m aligned with those who suggest that SONOS is not intended for your proposed use case. In fairness to SONOS, in 2005 when SONOS hit the market, WiFI was not as advanced as now and SONOS designed a robust multiroom wireless audio system that no one else was able to achieve. You may be familiar with the latest darling of WiFi -- the mesh. SONOS has used mesh since inception and has a ton of audio related patients in this area -- many now licensed to others. Starting fresh and using the latest WiFi6 and soon to be introduced WiFi7 SONOS could probably reduce the 75ms latency somewhat, but this would require abandoning the older WiFi4 and WiFi5 units already in the field. The reason for the 75ms latency is to give players some time to work around local interference issues. SONOS will rearrange the mesh topology as necessary to work around issues. Muting a player because of a nearby burst or new source of interference avoids unnecessary loss of audio. 

@buzz I get what you say. Of course, my Yamaha Monitor speakers are built for my live music usecase. So now I have sonos in my living room, and yamaha’s at my desk. You could argue this is the best setup.

Sonos is intended for multi-room usage after all. And I totally understand there has to be a delay to make this work reliable. Nevertheless, when only using one speaker (or 2+ when using Sonos Amp with wires speakers in 2.1 setup) connected via digital or analog input, there is simply no need for delay. The delay can be added as soon as needed: when streaming from or to other (grouped/stereo) speakers. For example: the sonos amp in 2.1 does not need any delay. As soon as you add rear speakers or group it with an other room. Then yes, you need the delay for it to function. 

To be clear, in your 2.1 setup, the 30-25 ms delay is needed to wirelessly communicate to the sub.  If you were using a wired sub, then perhaps not.

And to flesh out the stuff that John couldn’t think of offhand:

There is the HD Fury Arcana, the Feintech VAX04101k, and the latest, and least expensive, I think,  is the OREI HDA-935. Check your local retailers for availability, or Amazon. You can also order from those links from the companies directly, I think. 

It seems to me that you can have cheap, quality, and easy to use, but you can only have 2 of the 3.  I think there’s a saying in automotive circles similar to that.  Anyway, I think people tend to highly favor ease of use today and don’t always have much appreciation for quality, which is why the ‘impulse buy’ BT player exists.  You could argue it’s the motivation for the digital revolution to begin with, and quality has been playing catch up.

And really, I think you could add ‘snake oil’ to the list of options, but you can still only have 2.

Stop referring to a “digital input”.  The only Sonos devices with digital inputs are soundbars made for TV.  The others (Port, Amp, Five) are all analog inputs.

As to “The delay can be added as soon as needed: when streaming from or to other (grouped/stereo) speakers.”, you do know you can switch from a single speaker to a group of up to 32 speakers with a tap of the controller?  So how are you going to magically add a 75 ms buffer to that “standalone” stream without stopping the music?  The music playing seamlessly when grouping and ungrouping is part of the Sonos experience, stopping the music to build up a buffer is not.  

I specifically refer to my Sonos Amp which DOES have a digital AND analog input. It’s called HDMI and there is also a HDMI to optical dongle. And since the Amp is cleary made for a Hifi experience, why not offer Hifi-like 0 delay experience. 

And to answer your question: when I group I have to hold the play button and it takes ~2 seconds and and a confirmation ‘bleep’ before the device starts playing. So I guess it would not be that big of a problem that IF a standalone device is playing at 0 delay (because it’s plugged in via an analog or digital input), it would simply play a 75ms ‘bleep’ to confirm and to masquarade a pause. Heck, you wouldn’t even hear it if you are in a other room pressing the group button on a other device.

And to get back to a proposed solution using a Five; Since there have been no answers, I think no one knows if the Play:5 / Five standalone ‘workaround’ by disabling network connection actually works for everyone, or if it was just a bug.  

That’s a function of the long press on the play button, not the actual grouping.  If you group via the app, as most do, grouping is almost instantaneous and there is no ‘bleep’.  

It’s been answered before; the Five will have the delay regardless of the network connectivity.  The person claiming otherwise was just wishful thinking.  

Bottom line, if you need live performance type response, Sonos is not fit for purpose.  Find something else. 

If you’re going to split hairs, it’s an HDMI-ARC connection, not HDMI.  It’s using an HDMI cable but a source that outputs audio over the HDMI standard won’t be read by the Amp, It has to to output over the ARC channels.    And since HDMI-ARC was clearly designed for AV setups, and with view exceptions, only TVs generated the signal, it’s quite a stretch to claim that it’s to be used for straight audio sources.  Yes, you can use an optical dongle, but that was created for legacy TVs that are not HDMI-ARC compatible.  The fact that you this source is labeled as TV and can’t be renamed emphasizes this point.  Again, you might be able to use the Amp for unintended purposes, but that that doesn’t suddenly make it an intended purpose.

This is not a feature I would want instead of current functionality, and not something I would ever turn on.  I don’t want a moment of bleeps or silence every time I change the groupings in place.  As well, how would it handle the case where you go from a group to a single player.  Do you just skip 75ms of the audio?

I replaced my Sonos S1 system last week, which previously consisted of 3 Sonos Connect and a Sonos Connect AMP with Sonos Port and Sonos Amp. 
Why I did that I wonder now - maybe I just wanted to continue to support Sonos as one of the first users.
So now I have a new Sonos Amp in my home office. Here, my typical usage looked like connecting via line-in to the audio output of my notebook.
I played music mostly through the Windows Controller app and for video conferencing I use the line-in signal.
This worked wonderfully with the old S1 Sonos Connect Amp, but is NOT possible with the new device. 
The audio delay described here is a game stopper here. So this is what I spent thousands on - cool.