Cell Phone Mix Minus on Audio Mixer

In this post, I’ll show you how I made a very affordable cell phone mix minus setup with my analog audio mixer, and a few other components, to integrate my iPhone 8+ so that I could take live calls and use my studio microphone instead of the phone’s built-in microphone. This configuration is useful for podcasters who would like to take live calls during their shows, and also for recording phone calls (make sure you have the other party’s consent before recording!).

08 July 2020 – Written by Michael R. Myers #mykmyrs

Skill Level: Intermediate

What is Mix Minus?

Simply put, mix minus allows an audio configuration where the sound of the cell phone is played to the caller through an audio mixer’s output, but their voice input is “minused” out so that they don’t hear themselves through the output’s signal. If you don’t remove their vocal input from the signal chain, a feedback loop would be generated and they’d sound like they’re in an an echo tunnel. Unless you explicitly tell someone, they probably wouldn’t even know that you are processing the call’s audio.

You can read much more in depth here if you are interested in more usages and details regarding for cell phone mix minus.

What You’ll Need to Create Cell Phone Mix Minus

  • A older cell phone with a 3.5mm headphone jack, or a lightning port
  • An audio mixer with an FX Loop connected to your computer, either analog or USB. I use a Behringer Xenyx 1002 analog mixer in my studio.
  • A microphone connected to the mixer. I use a Pyle PDMIC78 in my studio.
  • An original iRig 1 guitar interface, or an iRig 2 guitar interface
  • For lightning phones, an official Apple 3.5mm to Lightning adapter
  • A mono 1/4″ TS guitar cable
  • A 3.5mm stereo audio cable with 2 separate 1/4” TRS plugs on the other end. I use the Pyle PCBL43FT6 in my studio.
  • Studio headphones connected to the mixer’s 1/4” jack. You may need a 3.5mm to 1/4″ TRS adapter
  • Optional
    • A boom arm with a shock mount and pop filter to hold your studio microphone so the call can be hands-free
    • An external recording device to allow for saving the conversation to disk
    • A USB audio interface to connect the mixer to your computer

Some Remarks Before We Continue

  • Newer cell phones, such as iPhones, only have a lightning port. You must have an official Apple 3.5mm to Lightning adapter. You can get these adapters for around $9 USD at Target, or buy online. DO NOT USE a cheap adapter because the cheap adapters only send stereo audio out. They DO NOT allow the microphone to be used, and you need to be able to use the microphone input of the cell phone.
  • While the 3.5mm to Lightning adapter is connected to your phone, you cannot charge or supply power to the phone. Make sure your battery is fully charged before starting a caller session.
  • When using an old Samsung Galaxy S4 cell phone, I can directly plug the iRig1 into the phone’s headphone jack it works perfectly for hearing and speaking.
  • Your audio mixer has to have an effects loop (FX Loop) or auxiliary send capability. Mix Minus will not work without this mixer feature.
  • Use a good-quality studio microphone with your mixer. Connect it via XLR if possible, and set the gain appropriately so that you input level is not clipping. Adjust any EQ knobs you like to shape your voice’s output sound. Condenser microphones would work great for voice. If yours requires phantom power, your mixer can provide it easily.
  • Most YouTube videos and online articles I read use the IK Multimedia iRig 2 guitar interface due to its TRRS audio cable (2 rings for stereo audio and one ring for microphone) and a built-in gain control knob. As of this writing’s date, IK Multimedia sells them for $39.99 USD. I had an original iRig guitar interface laying around and tested it and it works great for mix minus. It is missing the gain control knob that is present on the iRig 2, but you can use your mixer/USB audio interface to help with the gain. Check Amazon or eBay for the iRig 1 which is cylindrical in shape and offers a TS guitar cable input, 3.5mm aux cable out and a TRRS 3-ring cable.
  • You can find the 3.5mm to dual 1/4” TRS cable to connect to the headphone jack of the iRig to the stereo inputs of your mixer at electronics stores or online.

Steps to Connect the Cell Phone Mix Minus Cabling

  1. Connect your microphone to an available channel strip on your mixer. Try to use an XLR input if possible because they usually have a small gain knob to help you set your input to a strong level. Set its FX channel knob to the 12:00 position to enable sending its output to the mixer. Set its volume level knob all the way to the left to disable any audio output at this time. I pan my microphone audio 100% to the left.
  2. Connect one end of the guitar TS cable to the FX Loop output jack of the mixer. Connect the other end to the iRig interface’s 1/4” guitar input jack.Connect FX Loop to iRig
  3. Connect the 3.5mm to dual TRS cable to the headphone out of the iRig interface.Connect 1/4" to iRig
  4. Use the dual connector side of the cable and insert them into a channel on your mixer. Use the red cable as the “right” side of the stereo signal. Set its FX channel knob all the way to the left to disable it. LEAVE it disabled at all times, or the caller will receive a feedback loop. Set its level knob all the way to the left to disable any audio output at this time.Connect TRS to Mixer
  5. Connect the iRig’s 3-ring cable plug to the 3.5mm to Lightning adapter. If using a phone with a headphone jack, connect the iRig1 directly into the phone’s headphone jack.Connect lightning to iRig
  6. For phones that need a lightning adapter, connect the lightning adapter to the lightning port of the cell phone.
  7. Connect your studio headphones to the mixer’s headphone jack to monitor the call. Try not to use speakers/studio monitors if possible.
  8. Since I am sending my analog mixer’s output to two (2) input jacks on a USB audio interface for left and right audio channels, I have to enable the “2-TR TO MIX” button on my mixer so that the audio is sent from the computer back into the mixer while recording. If I do not enable this feature, I cannot record the call’s audio.
  9. I also have to pan the mixer’s audio input channel for the phone hard right so that I can boost the gain on my USB audio interface’s input 2 to get a nice, solid signal from the caller’s phone.
  10. My USB audio interface’s gain knobs are set at about 10:00 for channel 1 and 2:00 for channel 2. Understandably this is subjective information, but this produces a nice blend of my microphone and the caller’s audio.
  11. After recording, I have to disengage the “2-TR TO MIXER” and enable “2-TR TO CTRL ROOM” to hear the playback from my DAW where I recorded the call.
  12. Test the setup with a phone call to your cell phone from another person’s phone. Adjust your phone’s audio output level with the buttons on the phone. Speak into your microphone and verify your levels are strong and not clipping on the mixer’s signal meter. Use the level knob on the mixer to adjust the cell phone input channel. Usually around 12:00 will provide a strong signal to be able to hear the caller through your mixer.
  13. If you recorded the audio, it will end up being a stereo file, with your microphone on the left channel and the caller’s voice on the right channel. Using this method, you have distinct audio sources and you can separate and apply processing on the channels individually if necessary.

With an optional boom arm to hold your microphone, you may be able to leave your microphone set up so that you can do hands-free calling whenever you want.

Summary

Using a cell phone mix minus with an audio mixer is a great way to take live telephone calls for podcasters or to record telephone conversations. With a few more steps, you can integrate the mixer’s audio stream into a computer recording application, or an external recording device, and make permanent recordings of the phone calls.

If you would like to add to this content to help other folks, please contact me and let me know what you have in mind.