Wildlife Sound Recording Society

RememBird-X technical tests

RememBird records in MP3 format and operates at a fixed gain. For these tests the MP3 compression was set to 320kbps which was the highest quality available, and at 1kHz ± 100Hz. It has a fixed gain level, so the first objective was to explore the sensitivity and noise level. Noise is hard to measure in an MP3 device using analogue test gear as the compression can alter wideband noise, reducing it in parts where no signal tone is present. The results should be considered indicative. A test rig was prepared, which was the same as used to measure noise in HiMD. Attenuation of the rig is ~42dB

test setup

Fig.1: Test setup - the DC blocking capacitor is 4.7μF 35V + to D.U.T. to prevent excessive loading of the plug-in-power system.

A signal of 1.8mV rms was then presented to the attenuator, resulting in an input of 14uV (-95dBu)

RememBird spectrum at -95dBu

RememBird noise floor with -95dBu input (2.7Hz measurement bandwidth)

With its plastic case, there is some residual induced hum from the domestic wiring, since you have to bring your hands near it to press the momentary record button. Naturally in its intended working environment this is not a problem.

Sensitivity

A -95dBu input tone gives a -67dBFS signal, so the maximum input level (0dBFS) is -28dBu, about 30mV rms.

Noise

The MP3 compression is visible in that the noise floor drops ± 400Hz from the 1kHz tone. Taking the noise within this region, it is approximately -115dBFS ± 5dB. The measurement bandwidth is 2.7Hz, so scaling up to the 22kHz signal bandwidth means the noise is 39dB higher at -76dBFS Since the RememBird operates at a fixed gain level, this can be combined with the maximum level corresponding to 0dBFS at -28dBu to give a mic preamp noise level of around -104dBu ± 5dB. This is reasonable for the likely application.

To put this in perspective the RememBird-X would be used with something like the MKE300, which Sennheiser quote as a sensitivity of 16mV/Pa (-34dBu) and a 18dB (A weighted) noise level. Mic noise is therefore about -110dBu. The RememBird is therefore a little bit noisier than the mic but within 5-10dB of the mic self-noise. Experimentally, this is supported by the slightly higher high frequency noise you can hear on the Skylark recording compared to the same subject through the preamplifier.

Frequency Response

Better than 20Hz to 20kHz ±2dB (this is the measurement limitations of my test gear)

Plug-in-Power (RememBird-X only)

Ths was measured at 2.3V ± .1V and capable of delivering a current or 220µA. The available current is low so compatibility with any PiP microphone should be assessed beforehand. This was experimentally sufficient to power one channel of a FEL SJ3.5 preamplifier, though that is specified as requiring 300µA and the preamp is therefore operating out of spec.

You can read the manufacturer's technical specifications at

http://www.remembird.com/html/specifications.html

Return to RememBird review

bandwidth correction is 20*log(√(22000/2.7))
1Pa is about 94dBSPL so mic noise is corresponds to an SPL of 94-18 = 76dB down on the 16mV (-34dBu) at 1Pa. However, the characteristic of the noise is not known, so the A-weighting could flatter this by up to 5dB.

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