Using the DJ-Tech REC-IN as a line input device with SignalScope Pro


Recently I purchased the excellent SignalScope Pro app from Faber Acoustical, but to use this for serious measurement on an iPhone requires a dock device capable of providing a line-level input. The built in microphone of the iPhone is not suitable for measurement of signals with any significant low frequency content, as described in this post. However, one is not spoilt for choice when it comes to finding a suitable dock device. At the time of writing, Faber Acoustical recommend four devices but one is only available in Japan. After a bit of searching, I came across the REC-iN from DJ-Tech, which is available in the UK from Maplin Electronics for around £30. What you get for this is a fairly sturdily-constructed device with line input and output options, and recording level control. It is also capable of syncing and charging the iPod & iPhone.

Top and front views of the DJ-Tech REC-iN

The REC-iN is supplied with a number of cradle adapters, although the one for my devices (2nd gen iPod touch and iPhone 3Gs) was not a great fit, and did offer less support to the devices – especially the heavier iPhone – than I would have liked. My sample came with two apparently identical adapters of this size, so perhaps I am missing the proper one.

Audio performance
I have to confess that the name “DJ-Tech” didn’t initially inspire confidence in the device’s hifi credentials, but it sounds fine, outperforming the headphone output of the iPhone 3Gs when fed into a hifi system of decent quality [Pure Sound A30 amplifier & Linn Ninka speakers]. It is capable of making good quality recordings via the line input, provided careful attention is paid to the input level. In my experience it is best to ensure that the yellow -6dB light stays off (more on this below).

Measured performance
Frequency response is commendably flat over a wide range of input levels, although the channel balance varies when the input level control is adjusted.

Frequency response, and channel balance variation with level.

As mentioned above, it is best to adjust the input level control to ensure that the yellow -6dB light stays off, as distortion creeps in above this level. The image below shows the frequency response when the yellow light is solidly lit.

Distortion evident when input level is too high.

General notes

  1. SignalScope will not recognise the REC-iN as a line output device. Faber Acoustical advise that this most likely because this is an older design that is not capable of operating in line-in and line-out modes simultaneously. In practise this is not a barrier to using the device for measurement purposes, since the frequency response of the iPhone and iPod headphone outputs measures the same as the line output.
  2. Since it’s a dock cradle rather than a cable, turning the iPod on it’s side to view the graphs in landscape mode requires careful support of the iPod. This is something that became obvious as soon as I started using the device, but which had never occurred to me until that point. I tried using a dock extender cable, but even the fully-featured 17 core cable I ordered did not appear to support audio input.

In summary
The DJ-Tech REC-iN is a suitable device for performing real-time audio analysis using SignalScope Pro. In addition it serves as an iPod line output dock and provides sync and charging facilities, all at a reasonable price. If you can live with the need for caution when orienting the device to view graphs in landscape format then this device is well worth investigating.

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