Sound-Light Ideas

How to record audio with binaural mics (Roland CS-10EM) using a PCM recorder (Tascam DR-40X)

Hi spatial visitors! I’m reporting today the hassle I had when trying to record with the Roland CS-10EM microphone using the Tascam DR-40X PCM (WAV) recorder. Maybe this can be useful for someone who is on a similar quest.

CS-10EM_Tascam_DR40X
CS-10EM and Tascam DR40X

For some years I had this amazing Roland CS-10EM that records sound directly from your ears and I think they are very useful for recording the sound of multichannel installations and soundscapes. Obviously, as everyone’s head is different (HRTF) the accuracy of binaural reproduction will change from person to person, but it’s still quite good for recreating the stereo field and the spatial reproduction back to my own ears is perfect, so I think it’s quite a special microphone to have.

The way I used to do it before was through a simple Sony ICD-PX333 audio recorder. It worked fine, but there was no input volume control and the format was mp3 at 192kbps. As I was recently working on a more professional video recording of a multichannel installation, I decided this had to be done in a PCM WAV format. I wanted to use the Tascam DR-40X, as this is my main microphone for going out in nature and doing field recording. It allows 2 external inputs, so “why not?”, I thought!

The CS-10EM is a microphone that takes “plug-in power”, similarly to lavalier or electret mics. These mics usually require some low voltage to function and plug-in power is usually provided by some devices in a range of 1.5-9V. This is also known as “bias voltage”.

The Tascam DR-40X does not provide this kind of output voltage to power the external microphones. Instead, it provides 48V (or 24V) phantom power, which is the standard for condenser mics. Probably they could not add more circuitry to the DR-40X design and since they didn’t expect people to use this with lavalier or this binaural mic, they just ignored this possible feature. Other Tascam models also lack a plug-in power feature, except for the DR-10 line, which is designed specifically for the lavaliers.

DR-10
Tascam DR-10

My plan wasn’t to buy another portable recorder (and the DR-10 line seems overpriced). I prefer carrying a single portable recorder when possible and add external microphones as needed. So what could be done?

One possibility was to design a circuit to convert the 48V/24V phantom power to something between 2-10V (as the CS-10EM manual specifies). Googling a bit, I found someone looking for the same application in the Arduino forum. There I saw that using a voltage regulator (step down) maybe wouldn’t work (higher voltage regulators seem to require more current than what phantom power can provide). One schematic using a transformer was posted, but I didn’t have the time to build the circuit (plus adapting it to stereo) and test it.

Another discussion on StackExchange suggested a simple voltage divider to make it work. This would require testing, soldering connectors and making some sort of adapter. I wasn’t convinced this would provide a clean line output and considering I only had a few days to do this and I was super busy with other projects, I looked for another, quicker, solution.

I found the RØDE Microphones VXLR+ adapter, it converts 48V to 5V. I don’t know what type of circuit is inside, but it’s RØDE so I imagine it’s well-made. It’s a bit overpriced (£21 on Amazon UK in 09/2021), but it seemed convenient. The issue is that I had to buy 2 of them to connect the 2 channels. The XLR input fits fine the Tascam, but to join the L and R lines with the CS-10EM it was necessary a splitter/adapter cable. More specifically: Y splitter cable, 3.5mm mono (L and R) male to 3.5mm stereo female.

VLRX+
VLRX+

So I wasted a few more hours looking for this specific connector. I found one on eBay UK but it was 1.5 metres long! That’s bad for the sound quality and more wiring on the way. At home, I had a more conventional Y splitter cable, but it was 6.35mm, requiring more adapters, which compromises the sound quality and make everything bulkier. So I thought about soldering my own cable, but I don’t like working with 3.5mm sockets and my time was compressed..so finally, I found the right splitter on eBay from a shop (BestPlug) from Germany. A bit expensive (12.88€ / £11 with shipping and VAT ) but it looked good quality and it was only 15cm long, so I went for it.

Y Splitter 15cm
Y Splitter 15cm (BestPlug, Germany, Ebay)

Now I can finally record with those binaural mics on the Tascam, phew! This upgrade cost me about £55 and I know I could have bought another simple PCM recorder for less, like a Philips DVT1110 (£35), but as I said, I prefer to carry a single device for practical reasons. It seems a bit silly to use 2 adapters to step down the voltage since a single one would be more power-efficient, but for now, that has been my best option.

Finally, the results of 2x VLRX+ and the Y splitter are great. The sound quality seems perfect with no issues to note. If you have any better (or cheaper) ideas for connecting this Tascam with the CS-10EM, please leave a comment! 🙂

Tascam DR40X > 2 VLRX+ > 3.5mm Y Splitter > CS-10EM