All posts for the month June, 2024

Signal To Noise

This one is work related, and involves converting analog media to digital at scale. It’s been going on for many years, and that usually means that things have to change.

We initially used an elgato Video Converter for this task, with macOS, and it worked well for years. However, this was the only use of the iMac and we shifted the unit to a Windows 10 computer. It worked exactly the same and was reliable.

Windows 11 introduced some enhanced security including what they call Core Memory Isolation. This is a good thing, until the software you’re using wants access to that memory area and gets really upset when it doesn’t work. Elgato hadn’t updated the software, which is available on their website, in many years for the Windows users. It has updated it for macOS, but that’s not a path we’re going down.

Core To the Problem

So, the task of figuring out what to replace the elgato converter with was a few quick searches and two items were purchased. One half of this arrangement takes the composite video and stereo audio from the analog source and converts it to HDMI. These units frequently bill themselves as upscalers, taking a 480p signal and bumping it to 720p or 1080p. This is fine, but the video output we want is 640×480.

The second part is another device that intakes an HDMI signal and splits it into an audio and video stream. It’s very simple, and it works great in theory. There were some hiccups, however, and that’s where it gets interesting.

We needed to use different software for the video conversion, moving from the elgato software to OBS. It’s well-suited to the task, and with some simple instructions it was ready for others to use. Pick a video and audio source, change the resolution to 640×480, and start recording. Simple. It worked. Until someone compared video done with the new setup to the old one and raised a red flag.

Audio is the culprit here. No issues with the video, but there was something very off about the audio. I initially attributed this to reverb in a large speaking room on the tape in question, but when hearing the original transfer I got quiet. It sounded far better. This wasn’t just a small difference.

Cheap for A Reason

Interleaving is a way to do two things at once. In modern technology it’s most commonly been used visually with older televisions, where they would draw one line on the screen, skip the next, and then reverse the pattern the next time. It even got to the 1080i resolution in the days before LCD TVs were really good. Audio, however, is a format where it may have been used for years but only in the chain of processing. Not audibly.

Research into the HDMI-to-USB converter alerted me to some odd settings in the USB Audio Device that was shown in Windows. It was displayed as having 1 channel at 96khz. This was bad for two reasons: mono isn’t what I expected, and the sample rate was double what it should be. Others had noticed this and it seems that the audio chip on these devices interleaves the audio signal from left to right, meaning that there’s a stereo, 48khz signal in there but you have to process it to get that. This device had no drivers, nor were any seemingly available on looking.

I did find that some owners of components using this audio chip had written code that could untangle the two channels, and in testing I did find that it worked. However, due to the technical nature of the process I decided to pass on this as a solution. More research and I found that NZXT made a device called the Signal HD60 that not only had a page with specifications on a website, but stated its stereo output at 48khz.

A Fix

It was an easy install, and I tested it briefly and it sounded fine. To me. I asked that it be tested and around a week later I heard back that it sounded exactly the same. Dubious, I asked to be shown the new and old examples. They were right, and I was scratching my chin again.

Remember that there are two devices doing the conversion, one from RCA to HDMI, and the other from HDMI to USB. I’d only replaced one of these, and either or both could be the offending device. I did some quick looking through comments on the Amazon listing for the RCA device and audio was mentioned many times, negatively. Super.

So, now what do I do? Test to see if the NZXT device is truly passing DVD-quality stereo audio through? Test then again the RCA device to make sure that it’s at fault? Replace the RCA unit with something else? Yes?


I started by checking the old HDMI/USB adapter using an iPad with an HDMI output dongle. Inputting this to OBS resulted in no stereo recording while using a stereo panning video on YouTube. I tinkered with a few other things, but the audio echo and general sound were very familiar. Very bad.

That resolved, it was off to then test the NZXT Signal HD60 device in the exact same way. Similar video, but longer and with more range, performed as I’d hoped. Stereo separation and some of that neat psychoacoustic stuff to go with it. I expected this, so it was time to move on to the RCA/HDMI adapter.

Here’s where I had a short mental block, which lifted when I realized that I didn’t need to get video in to test, only audio. An older iPad, one with a 3.5mm headphone jack, and a cable with stereo RCA ends was all I needed to confirm what I suspected: the RCA/HDMI device had the same problem. It did not.

To my surprise, the RCA/HDMI adapter performed admirably. I wasn’t disappointed, because it meant that the problem was with the software. I asked for the original source material and did some live, monitored testing. I heard what I hoped to, and confirmed with the person responsible for the project that it was good. I then had them sign in to the computer and we repeated the testing on their OBS profile.

Ah Ha!

Some confusion set in when we monitored the audio and it sounded good, but when the recording was played back it had an echo. A quick search let me to a video explaining that it’s best to mute other input sources when recording or streaming from a single device.

Oh! Yeah. The thing I did on my profile but that we didn’t include in the instr for others…oops.

I did some more testing and found that it was indeed the Mic/Aux and Desktop Audio that were contributing to the audio and creating the echo. Muting those is very easy and a thing that I should have included in my instructions from the start.

A Releif

I was pleased that no additional hardware was necessary. Software can be fixed and reconfigured, and guides updated.

So, as a lingering lesson this should be something for people to keep in mind for solutions to problems that seem a bit to cheap compared to the brands with names you hear of.