5 January 2015
These small adaptors from C-Media; model CM119, are intended to provide stereo audio for headphones from a laptop or notebook pc that does not already have audio output, or which needs a 'better quality' output.
I bought one recently from Ebay to use in a project. It cost only NZ$16. The device is 'driverless'; any modern pc will instal a default driver for the device and on my Win7 pc, that was a straight-forward process. The device, when connected, then has an entry in the Windows Mixer. My pc uses the VIA HD audio deck, which, painfully, requires users to set the required device to be the default device before much happens. Windows presents it as a generic USB audio device. The Syba will handle 16 bit/44.1kHz (CD standard) and 16 bit/48kHz sampling only.
With sine-waves generated from 'Cool Edit Pro' I measured the audio outputs using the Praxis system. The results are not very good. While just adequate for my purposes, performance results would not satisfy anyone with discriminating hearing.
Audio output level into high impedance load is 0dBV (1 volt rms) for a 0dBFS (full-scale) input tone. This is ideal for line-level uses, but is loud on a pair of earbuds, when the pc source level is 100%.
Frequency response flatness: 40Hz to 12kHz is flat; 15kHz is -1dB and 20kHz is -12dB. There was no difference between 44.1kHz and 48kHz sampling rates.
Distortion: Although the audio harmonics were low, alas there are many aliasing (non-harmonic) products present, increasing in number and ferocity for primary tones above 5kHz. For a 5kHz tone, the THD+N is 1%.
The unit is cheap and it does provide the functionality. Do not expect audiophile quality. I may replace it in future, but at present it does the job adequately well. Listening to music on headphones, a certain edginess is apparent with a slight noise floor modulation effect.
Axino-Tech January 2015
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