Low/distorted signals from headworn microphone

Question

I'm producing a podcast with several speakers in the same room. I'm also a complete novice when it comes to audio engineering.

The Original Setup

Originally we used a Yeti microphone set to 'omnidirectional' in the middle of everybody. Now I knew that it wouldn't sound fantastic. We have a very lively discussion and people talk over each other all the time, which is often a pain to edit.

The New Setup

I did some research and eventually wound up with the following setup;

• Shure SM35 (one per participant), connected to a
• Shure RPM626 inline preamp (one per microphone), connected to a
• El-Cheapo 6m XLR cables I bought in a hurry (one per microphone), connected to a
• TASCAM US-16x08 (only one :P), connected to
• A MacBook Pro, running
• Logic Pro X

The Problem

I did a test run with the headsets and the audio I'm getting is really quiet and slightly distorted. Here's an image of the two outputs in Logic;

Top is the Yeti, bottom is the SM35. This is an example of a (rare) moment where only one person was speaking. I understand these signals are largely incomparable but in this scenario the gain pot on the 16x08 is 3/4 up and the gain on the Yeti is next to zero. The speaker is relatively quiet and sitting maybe 3.5 feet from the Yeti, while the SM35 is barely over a centimetre away from his mouth (the recommended distance according to Shure).

Not only is the audio very, very quiet I can hear the slightest bit of distortion in it as well.

So, I throw myself onto the mercy of SO - what should I check? Have I fallen into a common pitfall? Is it all functioning properly and I'm simply being too unrealistic in my expectations? Is it the SM35? Is it the preamp? Is it the cheap (-ish) cables? Are my sources too loud? Does my sample & bit rate affect my final audio recording (44.1/24-bit, I'm considering going to 96 for that extra bit of wiggle room)?

Answer 1

Here's some basic checks you can do at each stage. This applies more generally to pretty much any signal chain too. I'm sure if you go through and check everything, you will find a place where your preamp volume is too low, you have a bad cable, or you're not getting power to the mic, or something else simple along those lines. Your signal chain should be okay if used properly:

1) Microphone- the Shure SM35 requires 5V phantom power. Make sure it's getting this (although if even a weak signal is coming out it's probably getting at least some power). Your inline RPM626 preamp is responsible for supplying this power to the mic and it probably requires 48V phantom power from the Tascam's mic preamp to make this happen. Make sure this is on as well. If you don't have a multimeter to check if 5V is getting to the mic, try swapping RPM626s or headsets since it's very doubtful that all your units failed at once.

2) Cable- if you jiggle the cable and the level of your audio changes, you probably have a bad cable. These issues are usually very obvious. If Pin 2 or 3 on an XLR (or T/R on a TRS) is intermittent or disconnected, you will lose half your voltage so your signal will be about 6dB too low. If you start hearing differences in hum/noise as you jiggle, you may have an issue with pin 1 (ground or sleeve). It's very easy to test cables with a cheap cable tester like the Behringer CT100. Just plug them in and jiggle near the strain relief to check for intermittent connections. The LEDs will show you which pins may be getting disconnected or are shorting to others.

3) Preamp (on the Tascam)- make sure your preamp level is high enough. This is a basic check you should do before going and swapping anything. If you find yourself cranking the pre and only getting noise, then you have problems at an earlier stage. But if your preamp level is too low, everything before it could be fine and you just aren't sending enough of that signal thru the audio interface into your DAW.

4) Interface- make sure you are plugged into a microphone input as opposed to line, and 48V phantom power is turned on. This is also where you adjust your preamp level as mentioned above.

These are just some simple things to check but 99% of the time the solution to things like this is very simple. Hope this helps.