H
hyperesthesia
New member
Hi. I recently got a stereo A/D mic pre-amp from http://core-sound.com/HighResRecorderNews.html#MIC2496 It has an advertised noise floor
of -140dB (at minimal gain). However, when I began using the unit, I
started hearing an unusual pulsing in the output. A deep pulse around 500Hz. It sounds similar to a helicopter chopping away.
I ran the unit into Vegas, with all software meters at unity gain, and the
mic pre-amp at minimal gain. Vegas showed the noise floor at -70dB, as does
my soundcard at input.
I did this test by sending the data through the Coaxial S/PDIF output of
the mic pre, to the Coaxial S/PDIF input of my soundcard. I tried this with and
without my Rode NT4 mic attached. In both cases, I heard this pulsing. The sound gets
louder when I turn up each pot on the pre, and seems to change tempo
depending on where they are. It usually cycles around 5 times per second.
I also have a Nomad Jukebox 3, which records to 16/44.1 .Wav files. It
has S/PDIF input, and when I send the mic pre to this unit (using the pres Toslink S/PDIF output), the same noise
occurs. The pre has both coax and toslink outputs.
I sent the unit back, and was told it is working order with a noise floor
of -138dB at minumal gain, and that I was somehow measuring the unit's noise
inaccurately.
Here's an exerpt from their site on the units noise performance.
"Here's a plot that shows the noise performance of the Mic2496 with a 1.1 KHz (50 mV) signal at its mic input, sampled at 24-bits/96 KiloSamples per second, with minimum analog gain:
The noise floor is typically -140 dB, more than 120 dB below the signal -- very fine performance!"
I was asked by some if it was RF trash or local magnetic fields, but I tried moving around to different locations, and I got the noise regardless of where the unit is.
I'll receive the unit again shortly, so I can test it once
more. Am I missing something here? I'm no audio wizard, but I thought this
would be fairly simple to figure out. Please, any assistance is appreciated!
of -140dB (at minimal gain). However, when I began using the unit, I
started hearing an unusual pulsing in the output. A deep pulse around 500Hz. It sounds similar to a helicopter chopping away.
I ran the unit into Vegas, with all software meters at unity gain, and the
mic pre-amp at minimal gain. Vegas showed the noise floor at -70dB, as does
my soundcard at input.
I did this test by sending the data through the Coaxial S/PDIF output of
the mic pre, to the Coaxial S/PDIF input of my soundcard. I tried this with and
without my Rode NT4 mic attached. In both cases, I heard this pulsing. The sound gets
louder when I turn up each pot on the pre, and seems to change tempo
depending on where they are. It usually cycles around 5 times per second.
I also have a Nomad Jukebox 3, which records to 16/44.1 .Wav files. It
has S/PDIF input, and when I send the mic pre to this unit (using the pres Toslink S/PDIF output), the same noise
occurs. The pre has both coax and toslink outputs.
I sent the unit back, and was told it is working order with a noise floor
of -138dB at minumal gain, and that I was somehow measuring the unit's noise
inaccurately.
Here's an exerpt from their site on the units noise performance.
"Here's a plot that shows the noise performance of the Mic2496 with a 1.1 KHz (50 mV) signal at its mic input, sampled at 24-bits/96 KiloSamples per second, with minimum analog gain:
The noise floor is typically -140 dB, more than 120 dB below the signal -- very fine performance!"
I was asked by some if it was RF trash or local magnetic fields, but I tried moving around to different locations, and I got the noise regardless of where the unit is.
I'll receive the unit again shortly, so I can test it once
more. Am I missing something here? I'm no audio wizard, but I thought this
would be fairly simple to figure out. Please, any assistance is appreciated!
