NYS SPP-L1 : I use two of these at my studio to link rack units

Been using two of these units at my studio for 3 years now.

I actually gave it a 5-star review some time ago, but I recently found it adds noticeable distortion to the signal being patched through.

I did a pretty simple measurement always using the same patch cable, a sine wave generator in my DAW, and listening and checking the input signal with an FFT frequency analyzer.

My results:

1-When measuring directly from AD to DA I got a pristine clean signal.

2-When patching the signal through the NYS I got a lot of added harmonics.

3-This happened independently of sine wave frequency (tested from 20 to 20kHz)

4-Distortion only happened when the signal output was above -19dBfs

5-As the output volume increases the distortion changes, as in the harmonics are not the same as the signal get's stronger.

6-This is happening on all channels.

I don't know if it always distorted the signal or if it just didn't age well, but my studio is a dry smokeless place so either way if after 3 years it's malfunctioning it means low quality.

In conclusion, don't waste you money on this unit!