The Best Way to Use Dual Displays on M1 MacBook Pro

ohdarling
4 min readOct 30, 2022

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Photo crea!ted by DCStudio — freepik

What is the problem?

The M1 chip is a powerful SoC released in 2020 by Apple, and then I got a MacBook Pro with M1 chip last year, I love it because its performance and battery life.

I used to use a 15-inch MacBook Pro, and usually I use it with two 27-inch 4K displays in clamshell mode, but when I got MacBook Pro with M1, the problem happened, the second 4K display could not be driven.

I don’t know if this is a limitation of the M1 chip or restricted by Apple, but I have to resolve it or my second display will go to waste.

How to resolve?

The best and only solution to this problem is to use a USB display adapter, the best known of which is DisplayLink.

DisplayLink (formerly Newnham Research) is a semiconductor and software technology company. They develop the DisplayLink USB graphics technology, which is designed to connect computers and displays using USB, Ethernet, and WiFi. It also allows multiple displays to be connected to a single computer.

In short, DisplayLink can emulate multiple display devices in a system through a self-built driver and output data to an external DisplayLink chip via the USB interface and convert it to DisplayPort or HDMI signals to drive multiple displays.

Which chipset?

But DisplayLink has several chips to make USB display adapters, such as DL-5000, DL-6000, etc.

So how do we choose?

Let’s check the comparison table:

At this time, we don’t need to use chips that don’t support 4K display, so we should only check the DL-6000, DL-5000 and DL-1950 series.

After searching the online store, I found that there are more USB display adapter products with DL-6950 embedded, and DL-6950 also supports dual DP combined to support 5K display, so I chose this model for future expansion consideration.

How’s the Performance?

DisplayLink officially claims that the DL-6950 can support up to 4K resolution and 60FPS refresh rate, how is the actual experience? I tested it, and the overall experience is still acceptable in office scenarios.

I have prepared some tests to see if the DisplayLink actually performs as expected, including:

  • Display quality comparison
  • Display latency when system is idle
  • Display latency when playing 4K video
  • Display latency when playing 4K action movie

I wrote an app that only show a timestamp on the screen, so we can check latency between build-in supported external display and external display created by DisplayLink.

Display quality comparison

Using the DisplayLink monitor as a mirror of the external monitor with built-in support, we can compare the display quality of the two monitors.

It is hard to find differences between the two monitors and I don’t think display quality is a factor in deciding whether we should choose DisplayLink or not.

Display latency when system is idle

It is confusing why the latency is shorter when the system is idle, but we can assume that the DisplayLink external display latency is very short.

Display latency when playing 4K video

We will notice that there is a noticeable delay of about 20ms when playing 4K video.

This may be because DisplayLink’s driver has to compress more frame data when playing 4K video compared to the idle state of the system, which results in longer processing time.

Display latency when playing 4K action movie

Compared to normal 4K video, action movies have more frequent and dramatic picture changes, so DisplayLink needs to spend more time to process the data, and it can be observed that the latency has reached 74ms at this time.

Conclusion

After extensive testing, we can find that the performance and experience of DisplayLink is acceptable in most usage scenarios.

  • Display quality is enough with 4K resolution and 60Hz refresh rate
  • There is no noticeable delay on the DisplayLink display while browsing or working
  • DisplayLink is not suitable for use when playing action movies because the latency is too long
  • Same as above, DisplayLink is not suitable for gaming

In the end, the best solution might be to buy a new M1 Pro MacBook which has built-in support for multiple external monitors, hah.

I hope this article will be helpful to you.

需要中文版本?前往 https://xujiwei.com/blog/2021/07/m1-displaylink-testing/

References

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