Sensor and PerformanceThe Dream Machines DM6 Holey Duo is equipped with the PixArt PAW3335. According to specifications, the 3335 is capable of up to 16,000 CPI, as well as a maximum tracking speed of 400 IPS, which equals 10.16 m/s. Out of the box, six pre-defined CPI steps are available: 400, 800, 1600, 3200, 4800, and 6400 CPI.
CPI Accuracy"CPI" (short for counts per inch) describes the number of counts registered by the mouse if it is moved exactly an inch. There are several factors (firmware, mounting height of the sensor not meeting specifications, mouse feet thickness, mousing surface, among others) which may contribute to nominal CPI not matching actual CPI. It is impossible to always achieve a perfect match, but ideally, nominal and actual CPI should differ as little as possible. In this test, I'm determining whether this is the case or not. However, please keep in mind that said variance will still differ from unit to unit, so your mileage may vary.
I've restricted my testing to the four most common CPI steps, which are 400, 800, 1600, and 3200. As you can see, deviation is consistently positive and as massive as it is inconsistent. A poor result overall. In order to account for the measured deviation, adjusted and mostly accurate steps of 400, 700, 1400, and 2800 CPI have been used for testing.
Motion Delay"Motion delay" encompasses all kinds of sensor lag. Any further sources of input delay will not be recorded in this test. The main thing I'll be looking for in this test is sensor smoothing, which describes an averaging of motion data across several capture frames in order to reduce jitter at higher CPI values, increasing motion delay along with it. The goal here is to have as little smoothing as possible. As there is no way to accurately measure motion delay absolutely, it can only be done by comparison with a control subject that has been determined to have the lowest possible motion delay. In this case, the control subject is a G403, whose 3366 has no visible smoothing across the entire CPI range. Note that the G403 is moved first and thus receives a slight head start.
First, I'm looking at two xCounts plots—generated at 1600 and 16,000 CPI—to quickly gauge whether there is any smoothing, which would be indicated by any visible "kinks." As you can see, no such kinks are in sight, which confirms that there is no smoothing across the entire CPI range. We can also see that SPI timing jitter is quite low.
In order to determine motion delay, I'm looking at xSum plots generated at 1600 (first row) and 16,000 (second row) CPI. The line further to the left denotes the sensor with less motion delay. What can be observed here is behavior I've seen on several other 3335 implementations as well. Basically, latency is greatest upon initiating motion and continually decreases from there until a minimum is reached. At the onset of the plotted motion, the motion delay differential is 3 ms, whereas at the end of it, it is as low as 0 ms. The most truthful way to present this data is by giving a range; i.e., 0–3 ms. This is still the case at 16,000 CPI, as seen in the second plot.
Aside from occasional outliers, tracking still looks good in wireless mode.
I'm again looking at plots generated at 1600 and 16,000 CPI. Both plots display the same behavior outlined above. Keeping the motion delay differential in wired mode established above in mind, I can measure a wireless delay of roughly 1 ms.
Speed-related Accuracy Variance (SRAV)
What people typically mean when they talk about "acceleration" is speed-related accuracy variance (or short SRAV). It's not about the mouse having a set amount of inherent positive or negative acceleration, but about the cursor not traveling the same distance if the mouse is moved the same physical distance at different speeds. The easiest way to test this is by comparison with a control subject that is known to have very low SRAV, which in this case is the G403. As you can see from the plot, no displacement between the two cursor paths can be observed, which confirms that SRAV is very low.
Perfect Control Speed
Perfect Control Speed (or PCS for short) is the maximum speed up to which the mouse and its sensor can be moved without the sensor malfunctioning in any way. I've only managed to hit a measly 4.0 m/s (which is within the proclaimed PCS range), at which no sign of the sensor malfunctioning can be observed.
Polling Rate StabilityConsidering the DM6 Holey Duo is usable as a regular wired mouse as well, I'll be testing polling rate stability for both wired and wireless use.
All of the available polling rates (125/500/1000 Hz) look nice and stable.
For wired mice, polling rate stability merely concerns the wired connection between the mouse (SPI communication) and the USB. For wireless mice, another device that needs to be kept in sync between the first two is added to the mix: the wireless dongle/wireless receiver. I'm unable to measure all stages of the entire end-to-end signal chain individually, so testing polling-rate stability at the endpoint (the USB) has to suffice here.
First, I'm testing whether SPI, wireless, and USB communication are synchronized. Any of these being out of sync would be indicated by at least one 2 ms report, which would be the result of any desynchronization drift accumulated over time. I'm unable to detect any periodic off-period polls that would be indicative of a desynchronization drift.
Second, I'm testing the general polling-rate stability of the individual polling rates in wireless mode. Running the DM6 Holey Duo at a lower polling rate can have the benefit of extending battery life. As you can see, all polling rates but 125 Hz look nice and stable.
This test is used to indicate any potential issues with angle snapping (non-native straightening of linear motion) and jitter, along with any sensor lens rattle. As you can see, no issues with angle snapping can be observed. No jitter is visible at 1600 CPI or 3200 CPI. 16,000 CPI has significant jitter, but considering the lack of smoothing, it's still surprisingly well-controlled. Lastly, my sample has a completely loose lens.
Lift-off DistanceThe DM6 Holey Duo offers three pre-definied LOD levels to choose from. However, they don't seem to be functional, as I was unable to detect any actual difference in LOD height. At any setting, the sensor does track at a height of 1 DVD, but not at a height of 2 DVDs (1.2<x<2.4 mm, x being LOD height). Keep in mind that LOD may vary slightly depending on the mousing surface (pad) it is being used on.
Since mechanical switches are being used for the buttons in most computer mice, debouncing is required in order to avoid unintended double clicks. Debouncing typically adds a delay (along with any potential processing delay), which shall be referred to as click latency. As there is no way to measure said delay directly, it has to be done by comparing it to a control subject, which in this case is the Logitech G203. In wired mode, click latency has been measured to be +16.2 ms when compared to the SteelSeries Ikari, which is considered as the baseline with 0 ms. Coupled with the measured wireless delay of roughly 1 ms, click latency in wireless mode sits at roughly +17.2 ms. Please keep in mind that the measured value is not the absolute click latency. Comparison data comes from this thread as well as my own testing, using qsxcv's program.
The main button switches were measured to be running at 3.31 V. Since the logic is running at 3.3 V, I believe these switches to be running within specifications.