If you need to setup a mix-minus to record Skype for your podcast, this tutorial will show you the gear* you’ll need and how to connect it all together.
The basic concept of a mix-minus is to input multiple sources of audio into an audio mixer (your microphone, sound cart, phone messages, Skype, etc.) then send that audio back out to Skype, minus (without) the Skype caller’s voice.
This setup is achieved by using an auxiliary output to selectively send certain audio out of the mixer. If you send all the audio that is in the mixer, back to Skype, then the person on the other side will hear a feedback loop of their own voice. So we need to exclude (minus) Skype’s audio (the person’s voice) from going back into Skype.
Depending on your mixer’s manufacture, the auxiliary output may be labeled Aux, FX or Mon Send. They’ll all work as auxiliary outputs in this setup.
Before We Begin
In this tutorial, I’m using the Aux Send B (post-fader) to send my microphone and a sound cart (via Bossjock app) to Skype.
If your mixer has both pre and post aux faders (labeled Aux A and Aux B here), you can use either one. Don’t get too distracted by this part but here’s how they differ from each other.
A pre-fader (A) is unaffected by the channel’s volume slider/knob. This means that if you use a pre-fader then you cannot control the volume of the audio being sent out of the Aux Send (to Skype) by using the channel’s volume fader. This can be useful if you are changing each channel’s volume in real-time to affect the recorded. By using the pre-fader, you can set the volume levels for Skype and leave them unaffected by changes you make using the volume faders on each individual channel.
Using a post-fader (B) simply means that the audio passes through the individual channel’s volume fader before getting sent out to the auxiliary send. With a “post fader,” you must turn up both the Aux B send fader/knob on that channel and that channel’s volume fader in order for the audio to be heard out of the Aux Send channel. This can be useful if you want to affect the level being sent to Skype by moving each channel’s volume fader/knob.
It’s much more complex sounding than it really is and it will be explained again below.
Take your time. Pause the video following each step so that you can perform the setup on your own mixer as you watch. Replay as necessary.
When you’re ready to test your setup, Skype has a test calling service (echo123) that will allow you to place a test call as if you had an interviewee on the line.
Step by Step Mix-Minus Walkthrough with Photos
****KEY – Red Arrows = cable, Yellow Box = mixer input/ouput, Blue Box = Mixer Controls****
Step 1 – Mixer and Cabling
For a proper mix-minus setup you’ll need a mixer with an “Auxiliary (Aux) Send” (yellow box in image). These channels allow you to choose which individual channels (1-8 on this mixer) get sent out of the mixer.
The knobs pictured inside the blue box (click the image to enlarge) are used to effectively turn on or off the Aux Send for each channel.
In this setup, I’m sending out the audio coming into the mixer, minus the channel that has Skype on it (7/8).
This is demonstrated in the video by turning the Aux B for channels 7/8 all the way to the left so that none of audio on 7/8 is being sent out of the Aux Send.
The yellow box, in the above image, shows you where the AUX SENDS are located on this particular mixer. This mixer has two auxiliary outputs, one pre (A) and one post (B) fader. You only need one Aux Send in order to perform a mix-minus.
Each additional auxiliary output provides the opportunity to create another mix-minus setup within a single mixer. This is useful if you are trying to do a multichannel setup, separating various Skype callers onto their own audio track.
Cabling (get the correct cables)
Mike Phillips (@McPhillips) wrote an excellent article on choosing the correct cables for “Interfacing Skype with a Mixer.” Unfortunately the article is not online anymore but here is the relevant info regarding the cables that are best for this setup.
If you’re connecting your Skype computer to your mixer with analog cables, make sure you’re doing it correctly. Be aware that there is one little issue that can damage or at least compromise the performance of some computers.
THE INPUT SIDE
Most Internet broadcasters and podcasters are (or should be) using an auxiliary send on the mixer to send a mix-minus feed to Skype. That feed is mono. Most desktop and USB computer sound cards have stereo inputs. Skype really only looks at the left channel for its input, but some cheap, no-name sound cards may actually get the channels reversed internally. Therefore, it’s a good idea to feed to audio from the aux send on the mixer to both the left and right channels of the computer sound card.
In a typical installation, the cable needed will be a ¼” two-conductor (TS) cable plugged into the aux send on the mixer and a 1/8” three-conductor (TRS) cable plugged into the computer sound card on the other end. To get mono audio from the aux send to both stereo channel inputs on the computer sound card, the tip and ring (TR) connections on the 1/8” plug need to be shorted together. If you make your own cable, simply connect both of the left and right hot wires (tips) from the 1/8” plug to the hot wire (tip) of the ¼” plug. With a USB sound card, the inputs are often RCA jacks instead of 1/8” jacks. In that case, the hot wires of each RCA plug (tips) are also connected together at the tip of the ¼” plug.
You can “make” this cord by using adapters, but using adapters should be a last resort to getting or making the right cable. Every time you add a connection, you add a potential point of failure. Anyone who has used adapters on audio cables has probably experienced a flaky connection because of adapters. If you have had a problem yet, you will.
A good solution is to use the Hosa CMP-105 cable, (see below). The CMP-105 has a 1/8” TRS plug one one and and a ¼” TS plug on the other. The tip of the ¼” plug is connected to the tip and ring of the 1/8” TRS plug. The ¼” mono plug connects to the mixer’s aux out jack, and the 1/8” plug connects to the computer sound card. Even though Skype is mono and only sees the left channel of the audio input, the CMP-105 causes audio to appear on both the left and right inputs of the computer sound card. If the card is miswired internally, it doesn’t matter since audio appears on both the left and the right channel inputs. If the card is wired correctly, it simply ignores the audio on the right channel.
THE OUTPUT SIDE
Connecting the output of a computer or USB sound card to a mixer can be tricky. Like the input side, most computer sound cards have a stereo output. If you have a stereo channel on your mixer that you don’t need for a stereo source, get a 1/8” stereo (TRS) cable as above that has two ¼” mono (TS) plugs for the left and right channels. The Hosa CMP-159 is a good choice. Plug the 1/8” plug into the computer card, and plug the left and right channel mono plugs into the left and right inputs on the mixer.
Remember that since Skype is mono, it’s a waste of a stereo channel to use it for Skype. Most mixers have more mono channels than they do stereo channels. It makes sense to consider using a mono channel for Skype.
Unlike the input side, it is not a good idea to short the left and right channels on the output of the sound card together. The explanation is very technical (the output impedance of each output is lower than the other channel is able to drive without damage or distortion), and not every sound card suffers from the issue (for example, if the outputs have a series resistor). The CMP-105 used above for the input side should not be used to connect the output of the sound card to the mixer. That cord shorts the two sound card outputs, and that’s a bad idea.
A safe solution is simply to connect the left channel of your sound card to the line input of a mono channel on your mixer. If you want, you can get the same CMP-159 1/8” stereo to ¼” dual mono cord and connect only the left channel ¼” mono plug to the mixer. That is, you only connect the gray plug to the mixer. Leave the orange plug floating, but don’t let it short against anything.
The adapted cables you see me using in the video above, while not the best options, have worked fine for me. But as Mike points out in his article, anytime you use an adapter “you add a potential point of failure.”
I wish I had seen that article before I made my video. Take Mike’s advice and use the best cables:
From left to right, here are the cables and what they do in my setup:
- An XLR cable to connect my microphone (Heil PR40) to the mixer.
- The computer or device running Skype connects to channel 7/8 via the computer’s headphone output (I’m using an iMic for this but you can use the computer’s native input/output) using a Stereo Mini (3.5mm) Male to 2 Mono 1/4″ Male Insert Y-Cable.
- The mixer is sending audio to the computer’s input (provided again by an iMic (not required), in this case) via Aux B using a 1/4 inch Mono Male to 1/8 inch Stereo Male Cable.
- My iPhone (used here as a sound cart) is plugged into channel 5/6 via another Stereo Mini (3.5mm) Male to 2 Mono 1/4″ Male Insert Y-Cable. This sends additional audio (music, SFX, telephone calls, etc.) into the mixer and then into Skype for the guest to hear.
- The 3.5mm TRS to Dual RCA cable is used to connect an (optional) audio recorder to the mixer.
Step 2 – Plug in the Microphone(s) and Get Initial Levels
Here you see I’ve plugged in my microphone to channel one using an XLR cable. I’ve turned the gain knob (first blue box below the mic input on the mixer) to its center position and the fader for channel one (blue box, lower left corner) to the center as well.
I’ve also turned the fader for the “Main Mix” (blue box on far right, bottom) to the middle position. The Main Mix knob controls the overall level of all the audio being sent out of the Main Outputs. This is what will be going to your recording.
These initial settings are just a start to confirm that we’re receiving audio from the microphone into the mixer.
Speak into the microphone at normal levels to confirm that you are receiving an audio signal.
If you have more than one microphone, repeat the setup process.
To learn how to setup proper microphone levels for dialog, see this tutorial.
Step 3 Plug in Aux Send Cable to Mixer and Computer Input
The next step is to take a cable out of your mixer’s auxiliary send channel and plug that into your computer. This will be how Skype receives the audio coming from your mixer.
The red arrow indicates the proper cable for inputting audio into the computer. Referring to Mike’s article on cabling for a mix-minus it’s important to note:
Most Internet broadcasters and podcasters are (or should be) using an auxiliary send on the mixer to send a mix-minus feed to Skype. That feed is mono. Most desktop and USB computer sound cards have stereo inputs. Skype really only looks at the left channel for its input, but some cheap, no-name sound cards may actually get the channels reversed internally. Therefore, it’s a good idea to feed (the) audio from the aux send on the mixer to both the left and right channels of the computer sound card.
A good solution is to use the Hosa CMP-105 cable. The CMP-105 has a 1/8 inch TRS plug on one end and a ¼ inch TS plug on the other. The tip of the ¼ inch plug is connected to the tip and ring of the 1/8 inch TRS plug. The ¼ inch mono plug connects to the mixer’s aux out jack, and the 1/8 inch plug connects to the computer sound card. Even though Skype is mono and only sees the left channel of the audio input, the CMP-105 causes audio to appear on both the left and right inputs of the computer sound card.
Again, I’m using the aux B (post fader) to send audio to the computer. An another explanation of post and pre faders can be seen the end of the video which begins at 9:20.
In the video, you’ll notice that the input to the computer is being handed by a device called a “Griffin iMic.”
If your computer doesn’t have a 3.5mm microphone input (e.g. Apple Macbook Pro models later than 2011) then you’ll need a device like this to input audio from the mixer to the computer.
When you setup your Skype audio preferences, you’ll want to select this device as your “microphone input.”
Step 4 – Plug the Computer (Skype) into the Mixer
In the picture above, the iMic is being used as my ouput from the computer. This is the same as using your computer’s headphone output. Either one will work.
Plug a Stereo Mini (3.5mm) Male to 2 Mono 1/4″ Male Insert Y-Cable into your computer’s 3.5mm output and connect the two male mono 1/4″ plugs into a stereo channel on your mixer (right-side yellow box in image). If you don’t have any available stereo channels, just plug the left (grey) plug into a mono channel (left-side yellow box in image).
Skype is mono only so there is no advantage to plugging into a stereo channel on your mixer besides not having to leave the right (orange) 1/4″ lead dangling. That said, it is fine to leave it out just make sure it’s not laying somewhere that will cause it to short out.
An important note about the cabling in this step from Mike’s article:
Unlike the input side, it is not a good idea to short the left and right channels on the output of the sound card together. The explanation is very technical (the output impedance of each output is lower than the other channel is able to drive without damage or distortion), and not every sound card suffers from the issue (for example, if the outputs have a series resistor). The CMP-105 used for the input side should not be used to connect the output of the sound card to the mixer. That cord shorts the two sound card outputs, and that’s a bad idea.
A safe solution is simply to connect the left channel of your sound card to the line input of a mono or stereo channel on your mixer. …Get the CMP-159 stereo to ¼ dual mono cord and connect only the left channel ¼” mono plug to the mixer if inputing to a mono channel on your mixer. That is, you only connect the gray plug to the mixer. Leave the orange plug floating, but don’t let it short against anything.
Or, once again, if you have an available stereo input on your mixer, you can put the orange plug into the right side channel as indicated in the image above (right-side yellow box in image).
Step 5 (optional) – Plug In Any Additional Audio to the Mixer
If you have another source of audio such as a sound cart with music and effects, recorded audio files, etc., then you can use one of your remaining open channels to bring include that audio.
In the picture above you see I’ve plugged in an iPhone using a CMP-159 cable.
I’m using one of my remaining stereo channels because the app I’m using as a sound cart (Bossjock for iOS) will be sending music into the mixer.
Play your audio from any external devices and turn up your volume levels (blue box) to confirm you are receiving audio into the mixer.
Step 6 (optional) – Plug In an Audio Recorder to the Mixer
In this setup, I’m using an audio recorder to record all the audio being sent into the mixer.
Check the “alternative setups” section below to see how to record into your computer.
If you do chose to record into a computer, I would still recommend using an audio recorder to serve as a backup.
Having a hardware backup solution can save your recording if your computer crashes. It can be really painful to be 20, 30, 60 minutes into an interview only to lose it because your software or computer crashed.
In the picture above I’m using a 1/8″ stereo plug to dual RCA to output the mixer’s audio via the “Tape Out.” This will capture a recording of all the audio going into your mixer including the person on Skype.
Recording to Separate Channels
If you have a mixer that has either a FireWire, USB2.0, USB3.0 or Thunderbolt output, it likely has the ability to send all its channels separately to the computer and record multitrack audio to supported software. However, most analog mixers do not have these types of connections.
If you only have a stereo mix out of your mixer how do you record audio on separate channels? Panning.
It’s important to understand that because you don’t have a FireWire, USB2.0, USB3.0 or Thunderbolt output, you can only achieve a maximum of two separated channels. For many podcasters this will be enough because it’s just you (the interviewer) and Skype (the interviewee).
You’ll notice in the image above that channel 1 and channel 7/8 have their “pan” knobs turned all the way left and right respectively. Because you are sending a stereo mix (2 channels on a single track) to your audio recording software, you’ll need to create two separate channels by panning one channel hard left and the other, hard right.
For example, in the above image, the microphone on channel one will be on the left side of the stereo track and the Skype caller on channel 7/8 will be on the right side of the stereo track. The resulting audio file will look something like this:
Once you bring the audio into your editing software, you can break apart this stereo track to create two separate mono tracks each containing only the audio that was placed on each track as a result of using the pan knobs.
Now you’ll have much more control over the audio in post production because your voice is not mixed with the person on Skype.
Some examples of what this allows you to do in the edit:
- Apply different effects to each audio track – Each person’s voice is different. When you have separated audio, you get to process each track specifically for that person’s unique voice. Each channel can now have its own compression, EQ, etc., creating a custom sound for yourself and your guest.
- Remove unwanted sounds – Your interviewee might cough while you’re talking and you’ll want to remove that. Having them on their own track will allow you to remove any part of their audio without affecting your own. If you didn’t using the panning method to separate your tracks, you’d be left with all the audio on both tracks and you would not be able to isolate and remove unwanted sounds without affecting the other person’s audio.
- Creating cleaner audio – My audio editing workflow consists of removing the parts of an audio track where there is no talking. For example, if I’m asking a question and the interviewee is just listening, I remove that part of their audio. This also removes the noise floor (hiss) from their track thus making the overall mix cleaner. There are other ways to accomplish this such as inserting silence or using a noise gate or expansion, but in most cases I use this “checker boarding” technique.
- Fix cross-talk – If your guest speaks at the same time as you are speaking it can cause both or one of the person’s audio to get lost in the cross-talk. This always seems to be the case just as someone has made their most important point. Having each person on their own track allows you to shift the two pieces of audio on the timeline thus allowing each person to be heard. This is an incredibility powerful tool to have as an editor.
Recording Into the Same Computer That’s Running Skype
If you want or need to record your audio into the same computer you are using for Skype, you’ll need to run another audio feed out of your mixer and into another input on your computer to your recording software.
For example, you can take the Main Mix from the mixer and input that into your computer (using a separate sound card/input on your computer). That audio will be used as an input for recording software such as Audacity, Adobe Audition, etc. This input will contain all the audio going into your mixer including the person on Skype.
The key to this setup is that you have a second sound card. You need this because each piece of software you use (Skype, recording software, etc.) will need to have its own input.
If you are using only one sound card, both Skype and your recording software will only have one option to pull its audio from and as we learned in this tutorial, the aux send will not contain the voice of the person on Skype. Your recording software of course needs to have an input containing all audio.
If your mixer has USB output then the mixer becomes your second sound card and you can simply tell your recording software to get its input from the USB output. Skype would then still get its audio from the input on your computer that contains your aux send output from the mixer.
Recording with Two Computers
Another way to handle the recording of your Skype interviews, using a mix-minus setup, is to use two computers.
Having two computers allows you to dedicate one computer just for Skype. This allows all of that computer’s resources to be dedicated to Skype which may also help improve the quality of your Skype connection.
But primarily, using two computers allows you to send your aux send into the Skype computer’s input and the main mix from your mixer into another computer for recording the interview.
*Gear Used to Make the Video:
- Canon 60D
- Canon Normal EF 50mm f/1.4 USM
- Transcend SD card 16 and 32GB UHS1 Class 10
- Manfrotto 701 HDV Tripod
- Rode VideoMic Pro
- F&V LED Ring Light
- Sigma 30mm 1.4
- Heil PR40 microphone
- Bossjock App for iOS (recording and soundboard app)
- Alesis USB 2.0 mixer (this replaced the discontinued Firewire version I’m using in this tutorial)
- The stand holding the mixer is actually for laptops but works well with this form factor
- Griffin Technology iMic USB Audio Interface (for use if you don’t have a 3.5mm input into your computer)
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