Recording audio from an external microphone systems using a smartphone

A number of people have asked us about this subject so we thought you all may find this useful.

Most of you will make use of microphone systems connected to racks of equipment. You may also have a dedicated recorder, but in many cases these devices output very large files making it awkward to save and upload. Sometimes there are firewall issues that prevent uploading from Council networks, so it may be more convenient to produce recordings using a smartphones or tablet – if you would like to make recordings of audio through your PA system in this way, you face two challenges:

1 – making a physical connection between the audio equipment and your smartphone and tricking the smartphone into disconnecting it’s internal microphone in order to accept the audio from the PA system

2 – Setting the audio level correctly

1 – Create a Custom cable


This cable is designed to connect an Android or Apple device with a 4-contact 3.5mm TRRS mini-jack to a mixer with XLR balanced output. It is made from a standard 4-core TRRS lead with terminating/interfacing resistors installed inside the XLR plug.

XLR (audio source)             \              /                       3.5 mm Jack (SmartPhone) 
                 +----|47R|-----|            |---------------------o  TRRS Tip       (Audio L output)
                 |              |            |
                 +----|47R|-----|   4-CORE   |---------------------o  TRRS ring 1    (Audio R output)
                 |              |============|
 XLR pin 3 o-----+--------------|            |---------------------o  TRRS ring 2    (Common)
                                |            |
 XLR Pin 2 o----------|4K7|-----|            |---------------------o  TRRS Sleeve    (Mic input)

The three resistors above are mounted inside the XLR connector, with the cable to the TRRS jack wired as shown. One end of the resistors can be soldered onto the XLR pins and insulated to prevent contact with the XLR connector case. Wattage and tolerance is not significant (1/4W suggested). Strain relief must be provided; in particular it will be necessary to sleeve or otherwise secure the cable to the XLR cable clamp (which is typically designed for a larger diameter cable).

XLR Pin 1 and sleeve are not connected.


To connect a standard TRS output to TRRS microphone input, a dummy load is generally required on the TRRS end in order for the Smartphone/Tablet to detect the cable as a “headset” (i.e. both earphones and microphone).

TRS (audio source, mono)                                                  TRRS (smartphone)
  /\                                                                       /\
  ||-------------+--|4K7|-------+            +---|47R|---------------------||
  --             |              |            |                             --
  ||             |              |            +---|47R|---------------------||
  --    Ground   |              |            |                             --
+----+           |                                                         --
|    |           +---------------------------------------------------------||
|    |                                                                   +----+
                                                                         |    |
                                                                         |    |

At the TRRS end, the 2 audio outputs are loaded with 47 ohm resistors to ground, with the microphone input connected directly to the audio source (which must be of the correct level, and is assumed to be capacitively-coupled). A 4K7 (4700 ohm) resistor is connected between the the Audio output/mic input and ground, to provide the microphone load required to trigger the smartphone microphone detection.

The TRS side assumes a conventional mono source; some devices only drive T (tip) and R (ring) leaving S (sleeve) unconnected; in that case the ground wire on the TRS side goes to R (ring) instead of S (sleeve), or alternatively a mono plug (TS) used instead since a mono plug effectively connects R and S together.

The above circuit effectively constitutes a 0dB attenuator (ignoring the load presented by the 4K7 resistor).

2 – Setting the Audio Level 

The smartphone expects the following characteristics from any microphone connected to the 3.5 mm jack:

Consumer Audio
Nominal Level                 -10 dBV
Nominal Level,VRMS             0.316
Peak Amplitude, VPK            0.447
Peak to Peak Amplitude, VPP    0.894

With this set-up you can use any audio recorder app on your smartphone. We recommend the Audiominutes app (search Audiominutes in Google Play Store) which is free to download; saves files at a reasonable file size (27mB per hour) and in standard MP3 format.

Any questions? please feel free to contact us for more info.