Okay, like I said, I received the new iFi iSilencer+ today, and I was having trouble discerning by ear whether it makes a difference on my iFi iDSD Nano Black Series.
So I decided to do some measurements!
Any other measurements of devices like these that you're likely to find are going to have been conducted with equipment that analyzes the signal itself (rather than how that signal translates to headphone performance). I wanted to do something different for two reasons: (1) I don't have that fancy equipment, and (2) I wanted something that might be more representative of what I/you can expect in actual use.
So what I did was play a sine wave through my Sony MDR-7520 headphones, and I recorded the output on my ThinkPad T470s screen microphone (like I said: no fancy equipment). I generated a 1000 Hz sine wave in Audacity at 0.005 amplitude (0.5% of maximum amplitude). Why so low? I wanted to test the iSilencer+ in its true use case: USB power. To make sure that the Nano powers through USB when I unplugged the cable to add the iSilencer+ in-line, I needed to turn the volume knob all the way down to power it off, so that I could power it back on
after plugging the cable back in. This meant that the only way to maintain the same volume across the two recording conditions was to turn the volume all the way
up (i.e., hard stop when turning clockwise). The tone at 0.005 amplitude yielded a normal listening level with the Nano turned all the way up, so I used this level to generate the tone. Having such a low signal volume also lowers the SNR, potentially allowing any benefits of noise-reduction to be observed more clearly.
Recording and analysis were done in Praat speech acoustic software.
These were the steps of the process:
1) Generate a 1000 Hz sine wave (0.005 amplitude)
2) Play sine wave through iFi iDSD Nano Black Series (iEMatch output) and Sony MDR-7520
3) Place headphone pad over microphone (placement doesn't move between recordings)
4) Record signal at 22050 Hz for 10 seconds
5) Generate FFT spectrum
6) Plot log-transformed frequency spectrum (50 Hz - 10 kHz)
There are two plots attached here. The first one (iSilencer-1.png) shows the spectrum without the iSilencer+ in red and the spectrum with the iSilencer+ in blue. The second one (iSilencer-2.png) shows the spectrum with the iSilencer+ in red and the spectrum without the iSilencer+ in blue. What we're looking for here then is areas where the red noise rises above the blue noise in both cases.
Although I can't necessarily hear a difference, it seems pretty clear to me that the iSilencer+
is actually reducing noise in a real-world scenario: although the reduction in higher frequencies is quite small (yet apparent), there seems to be a good deal of noise in the 300-500 Hz range that is reduced at least a few dB. Conversely, there is a slight bit of noise
introduced by the iSilencer+ in the skirts around the 1000 Hz tone. Also, it may be hard to see in the plot, but iSilencer-2.png shows that the amplitude of the sine wave itself is slightly higher with the iSilencer+ in line. Keep in mind that the y-axis has the same scale for both figures, so what this means is that not only is the iSilencer+ reducing noise but it seems to increase the signal itself somehow (this may just be a spurious effect though).
In any case, even though I can't necessarily
hear a difference, my own tests have convinced me that the iSilencer+ does have some effect. The effect seems to be large enough, that I'm going to keep the iSilencer+ for piece of mind.
Another fine product,
@iFi audio!
