DIY Multiroom Audio Part 1: Hardware

A few weeks ago we hosted a small party at our apartment where we had a couple friends DJ in our living room. The night before an idea popped into my head: wouldn't it be cool if we could live stream the music they play to other rooms?

This obviously isn't a very revolutionary idea. And on the surface, it shouldn't be too difficult. We knew that everybody would be using a digital turntable plus a laptop with some kind of software to do the mixing. So, initial thought: stream directly from the DJ's laptop to other devices on our home network. I found that it's pretty easy to set up a point-to-point stream with OBS on the source and VLC media player on the target device. We tested it with my flatmate's laptop and – after troubleshooting some Mac OS audio mixing issues – got it working pretty well.

Then came the night of the party, and we quickly realised what we'd come up with didn't really work out as well as we hoped. First of all, it was a hurdle to install and set up OBS for everybody who wanted to play music. But more importantly, most people that day didn't actually want to connect their laptop to our stereo, but their turntable (which acts like an external sound card) instead. And you can't install OBS on a turntable.

I suppose you could say I got nerd sniped after this failed attempt. I figured there must be a way to stream any audio that comes out of our speakers in the living room to other places. Ideally at the press of a button.

The audio basis

Our home audio setup is fairly standard. We have an A/V-receiver (Denon AVR-S770H) that acts as an amplifier for external speakers and has many audio/video input sources you can switch between. It's also connected to our WiFi and has a bunch of "smart" features like AirPlay or streaming music from Spotify.

It also comes with its own proprietary smart speaker technology called "HEOS". One of the main features of HEOS is the ability to group multiple speakers on the network together (via an app) so that they're synced. For example, when you put our receiver and our Denon Home 150 (another smart speaker we have) in a group called "Everything", you can AirPlay music to "Everything" and it will be streamed to our living room stereo and the other standalone speaker at the same time.

Unfortunately and counterintuitively, this does not mean you can mirror any audio source across multiple HEOS devices. Basically, HEOS does not have an option to use the output of a receiver as a source for multi-speaker streaming since the receiver is itself treated as a speaker.

So, if the built-in software can't get the audio output to the place we want, we'll need to look to the hardware.

Options for hooking into amplifier output

Time to find a way to physically get audio output from the AVR back to a computer. Our AVR has 3 types of hardware audio outputs:

1. a 3.5mm headphone jack

This seemed like the most straight-forward option until I realised it mutes all other speakers when you plug something in there.

2. RCA pre-outs

There are two RCA ports that output the unamplified audio. RCA signals are analog so we can't connect them directly to a regular computer. Still, this seemed like a promising option. Unfortunately, both of these outputs on our receiver are mono (i.e. right + left channel combined) because they're meant for subwoofers, and subwoofers aren't stereo. You don't want that for a live stream to regular speakers, though.

3. Powered speaker outputs (speaker wire)

I mean, yeah, obviously. Running speakers is the main purpose of an amplifier and this one happens to be able to blast 7 of them with 80W of power each. But how do we get analog audio from a high-power speaker connection back into a (digital) computer?

Line Output Converters

After doing some research online, I learned about line output converters (LOCs). Essentially, you hook these up to your speaker connections in parallel and they convert the amplified analog audio signal to a lower voltage suitable for RCA cables. They even have an impedance matching mechanism so your speakers don't get overpowered by high current.

Apparently, LOCs are mostly used by people who want to add active subwoofers to their car's sound system. But the principle there is the exact same as with our AVR – you want to get a readable audio signal from the line output of an amplifier. The best part is that these things are pretty cheap. What I ended up buying only cost 17 €.

Analog-Digital Converters

OK, now I can hook up an LOC to my stereo outputs and get 2 RCA outs (one for each channel). As I said, this signal is analog and thus cannot be processed like a digital audio stream directly. What we need in between is another hardware component, an analog-digital converter (ADC) which feeds the digital audio into a computer as an input device. (Important to note here is that this is not the same as a digital-analog converter).

And again, to my surprise, this is another piece of fairly cheap equipment. What I got was 19 €. It has 2 channels of RCA input and a USB connector that transmits the digital audio and also provides power. There are even a couple of monitor outputs, but I have no need for those right now.

Final setup

So the final setup is: AVR (stereo speaker wires) ➡ LOC (RCA) ➡ ADC (USB) ➡ computer. Since we already have a small laptop hooked up to the AVR as a media server, we just feed the digital audio back into that. Which means that if we play something from the laptop on the AVR, we've essentially constructed an elaborate audio round trip: what comes in through USB is what went out through HDMI.

It's also a nice way to test the loss of quality through this whole procedure. Here's the first 30 seconds from Earth, Wind & Fire's Getaway, first in original quality, then round-tripped through the amp and chain of converters.

Directly ripped from an official CD (16/44 FLAC):

ADC input recorded via Audacity:

The most notable difference between the two was the volume. The roundtripped recording was a decent bit quieter, so I added a bit of digital amplification for better comparison. Other than that, I think it sounds pretty close!

This concludes part one of our DIY multiroom audio setup. I've managed to get the audio (any audio) out of the amplifier and back to a computer, but how does one send it to other computers – in particular our smart speaker – on demand? That will be the topic of the second part. Stay tuned!