WA8LMF Home Page | Main Ham Radio Page | Soundcard Interface Page | Updated  21 October 2012

iMic USB Sound System

Despite the name, the Griffin Electronics "iMic" is not a microphone. Rather, it is a USB-connected basic two-channel-stereo "sound card".   It was originally intended to provide high-quality analog audio capture for the early Apple "iMac" computers. 

It also works perfectly on PCs running Windows 2000 or later where it shows up in the Device Manager as a "Generic USB Sound Device" or "iMic USB Sound System".    No explicit driver install is required in Windows systems; just plug it into a USB port. The Windows generic "class driver" for USB sound is "auto-magically" installed and enabled.

This device makes an excellent building block for amateur radio "sound card" applications.  Having a completely-separate second sound system on a PC, exclusively for ham operations, avoids accidentally transmitting Windows sound effects, music, instant messenger alerts and YouTube sound tracks over-the-air.  Not to mention that you can conduct on-the-air operations, and a Skype or EchoLink conversation simultaneously!   Further, the performance of this added sound system is, as described below, far superior to the original sound system on most motherboards. 

Current versions of most ham sound card applications such as DigiPan, MixW, mmSSTV, EasyPal, APRS Messenger, AGW Packet Engine, EchoLink, etc allow you to specify which sound card to use, if your system has more than one.


The device has a single "line-level" output (i.e. "playback") jack with a maximum output level of about .8 volts. (It can just about produce "0 VU" or "0 DBM" into a 600-ohm line, or drive any amplified speaker system to full output.).

It also has a single stereo input ("record") jack that can be switched between mic-level sensitivity (5-50 millivolts) or line-level (100-700 millivolts). This done with an actual mechanical slide switch (not a software virtual switch!) on the side of the unit.  The switch apparently inserts an attenuator in series with the low-level input.

In the mic-in mode, the device is sensitive enough to work directly with the typical 20-50 millivolt output of an FM receiver's discriminator.  In the high-level mode, the sensitivity is a good match for the output of the 6-pin mini-DIN "data" or "packet" jacks on many transceivers.  The mini-din "data" or "packet" jack  (actually fixed-level AUDIO connections rather than actual DC logic level data)  typically outputs audio levels similar to line-in/line-out RCA jacks on home stereo equipment.

The iMic is sensitive enough (in it's mic-level-input mode) to directly connect a turntable with a magnetic pickup cartridge (i.e. without a preamp).  Some audio recording/editing applications, such as the freeware open-source Audacity, can then actually apply RIAA phono equalization in software.

The performance of this device is vastly superior to most built-in sound systems on PCs.

[Classic hardware "Soundblaster"-type add-on cards have dedicated hardware and accurate crystal-controlled timebases to determine the sampling rate of the analog-to-digital conversion.   Current severely-cost-reduced motherboard-based "AC97" sound systems are "brain-dead" devices.  Massive chunks of software, running on the host CPU, simulate the missing dedicated hardware.  The sample-rate timing is derived from CPU interrupts, rather than from a dedicated oscillator.  The sample rate actually varies as the CPU loading changes (i.e. how many other programs are running on the PC competing for CPU interrupt services).  Further, the unpredictable latency of CPU interrupt service routines creates phase jitter in the sampled audio.]

Phase jitter and timing errors don't have much effect on MP3 playback (although some musical types with a sense of perfect pitch CAN hear the errors)  or the sound effects that punctuate Windows error messages --but-- they do have a major effect on the performance of amateur radio "sound card" applications such as SSTV, PSK31 and WSPR.  Weak signal reception of these modes is significantly improved with a good stable low-noise hardware-based sound system such as the iMic, compared to cheap motherboard sound systems.

Ham sound card programs frequently have setup options to enter correction factors for the sound card sample rate error.  These corrections can often run to hundreds or even thousands of parts-per-million for the typical motherboard sound system. (And then it keeps changing with varying software loading on the CPU!)    Out-of-the-box, the iMic was within 2 PPM.


As of the time of writing, the iMic sells for under USD $30.   The manufacturer's web page is here:


At the current time, the least expensive place to buy one is Amazon.com. This is the page for the iMic on their website: