Two PCs, One Stereo: How to connect multiple PCs to a single audio source

Hey, I'm Dave. Welcome to my shop. I'm Dave Plamer, a retired operating systems engineer from Microsoft going back to the MS DOS and Windows 95 days. And today, we're going to tackle a surprisingly common problem with a surprisingly uncommon solution. How to connect not one but two computers to a single set of speakers or to a single stereo system. Now, at first blush, that might not sound like much of a challenge until you actually try to do it. Because if you've got two PCs and one monitor, you've probably got a KVM or at least an HDMI switcher that lets you share the display. But when it comes to audio, things can get complicated fast. Now, the very simplest way to do it is to play the audio that you care about over the HDMI output into the monitor. And that will even follow your active system if you switch sources with a KVM. But it requires two assumptions. First, that your monitor has speakers. And second, that you're willing to put up with them as your main audio source. Let's assume that you want more. You want to feed your PC audio out to some powered monitors or to a bookshelf system or even to an entire component stereo. With a single computer only, it's pretty trivial. But once you've got multiple sources and a single set of speakers, things get more interesting. What if both machines need to play sound at the same time? What if one's a Mac and the other is a Windows box? What if you want to use Spotify on one and game audio on the other or run dual streams for debugging AVNC? That's where it gets complicated. But it's okay because there's an easy way to do it. And then there's the right way, and I'll show you both. The easy way, well, it's entirely software and it costs nothing, requiring no soldering, and it works beautifully under a very specific set of conditions. The right way, well, that one goes digital to digital over spitf optical audio and runs through an external audio interface. It's more robust, more flexible, and yes, a bit more expensive, but you'll walk away with full perfect fidelity, full control, and an understanding of how to tie it all together like a pro. And if neither of these solutions fits your needs, I'll show you the compromises in between that you can achieve quickly and easily with analog audio. And to do that, we're going to need to get a little nerdy. We're going to look at the origins of SpitF, which makes digital audio tick, and why your $800 sound interface might just have the same plug as your $29 DVD player from 1998. We'll even talk about the KRK Rocket speakers, and how many of mine have already failed out of warranty. But let's begin with a simple zerocost solution that works surprisingly well under one very big condition that you're using an app that supports remote playback control like Spotify. Here's how it works. Let's say you've got a Mac Mini hooked up to your monitor and studio monitors through a USB or Thunderbolt sound interface. That sound system is your one and only audio output. Now imagine you're sitting at your PC across the desk, maybe running Windows 11 or iuntu or whatever minty flavor of Linux is trendy this week. You want to listen to music on your PC, but you want the sound to come out of the Mac speakers. Well, with Spotify, you can do exactly that. Once you've installed the Spotify client on both machines and logged into the same account, you can treat them as remote playback targets. So, while you're sitting at your PC or even in Spotify on your phone, you open up Spotify, start playing a song, and then using a little playback target button, you send the audio to your Mac, and Spotify handles the rest. And that means it plays through your shared speakers as clean and clear as if you would hit play locally. The volume also remotely controlled. Play, pause, skip, no problem. You can even add songs to the queue from the PC over the network. While the Mac does all the heavy lifting. It's clean, it's simple, it's elegant, and it's totally free. But it only works for Spotify, and that's the catch. If you want YouTube audio for one machine and your game audio from another, well, forget that. If you want to watch your Netflix on your Windows machine and still hear the Mac OS system sounds, no dice. So, this isn't a general purpose solution. It's a clever workaround built on the specific capabilities of a specific app. But if you want everything from both machines to go through one set of speakers, regardless of what app or OS it originates from, well then it's time to level up. And to do that, well, we'll need to talk a bit about digital audio, specifically Spitf. Now, Spitf stands for Sony Phillips digital interface format. And no, I didn't make that up. It really was a standard by Sony and Phillips, dating all the way back to the era when CD players were still exotic and laser disc sounded like the future. It comes in two flavors. One's electrical and the other is optical. The electrical variant runs over coaxial RCA cable. Yes, the same kind you used for the yellow composite video on your Commodore 64 back in the day. And it uses a 75 ohm impedance standard. The optical version runs over tosslink, which uses pulses of red laser light beam through plastic fiber optic cable. Same data, different media. But here's the kicker. Spitf is digital. That means the audio signal is transmitted bit perfect. No analog conversion, no interference, no noise floor. As long as your cable works, your signal is literally flawless. It's basically a light pipe for PCM audio. And if your receiver, say a sound interface or mixing console, supports it, you can pull in a stereo audio signal from a second computer and mix it with your primary system seamlessly. And that's exactly what I do. You could also do it over the copper version of Spitf using that RCA cable, but somehow the optical variant just feels better to me. But the reality is that the bit rate is so low on this signal that Spitf is nowhere near to the bandwidth limits of the cable. No matter which version you wind up using, my setup uses an Apollo Twin X from Universal Audio. That's my main studio interface. It connects to the Mac via Thunderbolt directly into the PCI bus and it's the primary audio device for both Mac OS and Logic Pro and Final Cut and everything else. But it also has a spitf optical input and a lot of PCs already feature a spitf output as did my old Thread Ripper. But when I replaced the venerable old machine with a new HP mini PC, I found that it did not have a native spitf output on the back. So I went to Amazon and I picked up this USB to spitf cable and it works great. I'll put a link in the video description. Long story short, it plugs into any available USB port on your PC and the other end is a digital optical spitf cable ready to plug into a stereo receiver or in your case into your other sound card. It required no driver or installation and simply appeared as a new sound device in Windows. I set it to be the default output, plugged it into the Apollo Twin, and I had audio in under like 10 seconds. That USB sound card takes the Windows audio stream, games, YouTube, Discord, whatever, and spits it out digitally over Spitf. From there, the Apollo takes over. It receives the optical signal, mixes it with the Mac's native Thunderbolt audio, and outputs the combined mix to my studio monitors. Now, those actually go through a splitter, which splits it into four channels because I have four, and there's an equalizer before that. A lot of blinking lights and a lot of little knobs to play with at my desk, but no noise, no ground loops, no lag. And best of all, one big aluminum volume knob on the Apollo Twin X controls the output from both systems at once. Need to mute the Mac? Done. Want to hear just the PC? Well, solo with a spitf channel. Everything is routed in real time through the onboard DSP of the Apollo. It's studiograde signal management, and it makes life in a two PPC shop not just possible, but civilized. Now, I'll admit it. The Apollo is not cheap. Certainly not walking down the aisle at Best Buy with the wife cheap. But you don't need an Apollo to make this work or I never would have done this episode. There are dozens of much cheaper interfaces with spitf inputs that can mix audio from multiple sources. From MOTU or MOTU, from Focus, right, RME, they all make gear that can do it. Even some consumer AV receivers support optical input switching. And while that's not quite the same as mixing, it does let you toggle between inputs with a remote control. But what if you don't want digital audio? What if you're on a budget? Or what if you just don't care that much? Well, then for you, there's analog. If you're lucky, your monitor itself has an analog audio output. And if you're really lucky, it's a line level output. Then you simply connect to your PC via HDMI and run the monitor's output into your speakers or stereo. But the sad reality is that most monitors do not have a line level analog output. And in that case, the old trick is to simulate what I do optically, but to do it analog. You can use a simple stereo 3.5 millimeter line-in cable for one PC's output to the other PC's input. So, your first machine might output its analog over the standard green 3.5 millimeter jack, which then plugs into the pink line in on the second machine or vice versa. You might not even need any software at all, as some sound cards will automatically mix the analog input into the final output. It works. It's not lossless, and it does carry some noise, especially if your onboard sound card isn't that well shielded. But for most uses by most people, it's good enough. What you do not want to do is to split the analog signal from the two machines and combine them passively using a Y cable. It's a rookie mistake and it can damage your sound cards. Why? Because, well, when you connect two outputs together through a passive splitter, you're essentially shorting their output amplifiers against one another. One machine tries to drive the signal one way and the other machine tries to drive it the other way, and they fight. And well, they may not blow up instantly. It will degrade the sound and can permanently damage your hardware over time. So, you want active mixing, not passive combining. Thus, if you're going to go analog, use one systems line in to receive the other systems line out. That way, the signal only travels one way and each side is doing what it's supposed to do. You can even just grab a little $20 USB mixer off Amazon to blend the two signals manually. It's not pretty elegant, but it also works. Now, you might be wondering, what about latency? Well, with digital spitf, latency is basically negligible. It's just clock sync and bitstream decoding. But with analog line in, there's usually a small buffer delay, especially if a signal goes through software processing or volume normalization. And that delay could be as much as 100 milliseconds, which is fine for music, but can be distracting for gaming or video. So, if you're a gamer and you're trying to route your teammates chat through game audio and through another machine, digital is the way to go. Speaking of gaming, this setup actually lets you do something cool. You can run your game on the Windows box, route the audio to your Mac via Spitf, and then stream or capture everything on the Mac while keeping your system resources free on the PC. That's the same basic concept behind using a capture card for video, except now you've got the audio side sorted out as well. And if you're using something like OBS or Streamlabs, you can even monitor, mix, and record both sources in real time. It's a clean, flexible solution that scales with your setup from a couple of laptops to a full-on home studio. So the right way to do it is to go digital. Use spitf optical out for one machine into the sound interface of the other. But again, for most people, analog is going to be good enough. But whatever you do, use a line in, not a splitter. And whatever you do, don't try to run two systems into one speaker set using a $5 Y cable. That's the audio equivalent of plugging two power cords into one outlet with a paper clip. It might work for a while, I guess, but pretty soon it will look like somebody has crossed the streams. Thanks for joining me out here in the shop today. Be sure to check out an episode of Shop Talk where we answer the week's best viewer questions every Friday night on our second channel. If you don't know about the second channel, Dave's Attic, do me a favor and head on over to the link in the video description, check out an episode, and ideally get subscribed. In the meantime, and in between time, I hope to see you next time right here in Dave's Garage. >> Do it. Do it. Do it.

Dave explains a range of options for connecting mulitple computers to a single audio system. Free Sample of my Book on the Spectrum: https://amzn.to/3zBinWM Check out my new merch store at: http://davesgaragemerch.com/ Check out ShopTalk, our weekly podcast, every Friday! https://www.youtube.com/@davepl Apollo Twin X Duo: https://amzn.to/4p33jpK USB to SPDIF: https://amzn.to/4g4ic7o Stereo Audio Mixer: https://amzn.to/47oQHTE USB SPDIF Input: https://amzn.to/4mJ8uda Super Cheap DAC: https://amzn.to/465damB