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iMic (Third Version) 20 bit / 48 kHz (ASIO driver):

iMic (Third Version) 16 bit / 48 kHz (ASIO driver):

iMic (Third Version) 16 bit / 44.1 kHz (Apple Sound Manager Driver):

A comparison of the three plots above shows that using the 20 bit mode of the iMic makes no difference in the performance when compared to 16 bit (the noise floor and distortion are essentially identical). The performance of the Apple Sound Manager USB audio driver at 44.1 kHz / 16 bit also is equivalent.

iMic (First Version - full duplex):

CoreAudio Measurements:

iMic (Third Version) Input 20 bit / 44.1 kHz:

iMic (Third Version) Output 20 bit / 44.1 kHz:

iMic (Third Version) Full Duplex 20 bit / 44.1 kHz:

Measurement conditions:

• Measurement software: Mac the Scope, 2048 point (X2) FFT, Cosine window function, linear frequency axis.
• Stimulus signal was generated by Mac the Scope / Waavebox. Signal: 1 kHz, DIGITAL LOCK enabled, 1024 sample latency (e.g., sequence length).
• A pass-through stereo miniplug cable was used to connect the sound input and output jacks (full - duplex signal generation and measurement).
• iMic sound input gain switch was set to Line position.
• Reference Measurement device for CoreAudio input and output tests: LynxTWO

iMic tested was a sample of the original version. Distortion measurements of the revised version were similar.

Note: the distortion measurements may be replicated with the free, demo version of Mac the Scope (the session timeout limit provides ample time for making the measurement).

• Here is the effect of sample rate and input gain setting on the iMic performance.
• Here is the effect of the iMic tone controls on the iMic frequency response.
• Here are frequency response measurements for the above products and an explanation of the different iMic versions.
• Here are links to some other measurements.
• Here is a procedure for making the distortion measurement.

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