Hi-MD & Low Noise Field Recording

How quiet is the HiMD mic preamp? Sony doesn't publish noise of gain specs for their consumer grade mic preamps. EIN estimates by Bruce Wison, Richard and John Beale of the naturerecodist list and soundfile comparison tests suggest a value is somewhere between -110dBu and -124dBu. What do these numbers mean? We know the Hi-MD mic pre is noticeably quieter than some older MD recorders (hear one example). We know that there are very slight, audible increases in noise when progressing from the $2400 Sound Devices 722 recorder ( rated at-128 dBu EIN at full gain) to the $800 Sound Devices MP-2 (rated at -126 dBu EIN) to the Rolls/HiMD mic pre (hear these steps). It seems to be safe to regard the Rolls/HiMD mic preamp combo as quiet enough to use with a mic with an effective EIN of -110 or lower. This can be computed for any mic using the manufacturers' self noise and sensitivty ratings and Rane Notes 148 Table 3. The Sennhesier MKH 40, for example, with a self-noise rating of 12dB(A) and a sensitivity rating of 25mV/Pa computes to -110dBu. In order for the mic pre to not contribute noise, its noise performance needs to 7-10 dB(A) lower, For the MKH-40, a mic pre with -117 dBu to -120 dBu would be required. Soundfile tests I have done suggest that the self noise from the Rolls/HiMD mic pre is barely detectable above that of the MKH 40. Noise performance of this caliber in a consumer grade recorder is quite remarkable. Unlike many of the hand-held flash recorders which are designed primarily for voice, music and loud effects, the mic preamp in the Hi-MD recorders pre can provide 75dB of gain-- about 5 dB more than a Sound Devices 722 recorder. The input stage of the Hi-MD recorders is based on the Asahi Kasei AK5356 20 bit ADC mic pre chip. AK5356 Spec Sheet and AK5356 discussion. If you are considering a recorder to use with mics that have extremely low self-noise for recording ambience in quiet locations, the noise plots for the Rode NT1-A mic on this excellent PDF by Raimund Specht show the critical relationship between mic sef-noise and recorder mic preamp noise. My thanks to Raimund Sprecht, Dan Dugan, Klas Stranberg, Eric Benjamin and many other recordists in compiling this information and confirming results in the field.