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External voltage distance and the graphics card
The second point why I think onboard sound is problematic is the current graphics cards and their interaction with the analog audio branch. After all, the signals must somehow be processed and amplified in analog form after the DAC. Here the industry likes to advertise with high-quality capacitors and other stuff, but often enough forgets about elaborate shielding and consideration for the practical circuit board layout. You don’t believe that?
For a better comparison, let’s first start in absolute idle mode, where nothing moves on the screen and even the mouse has a transmission pause once. What we now see as measurement curves is the so-called extraneous or interference voltage. Transients can even be cruel! Here, too, I do not claim laboratory accuracy with the rather simple test setup, but it is always accurate enough to be able to make a reliable statement. The volume control is in the position where the distortion-free maximum level was previously determined.
With approx. 0.0025 Vrms at 500 ohms, the ratio is approx. 1:500 to the maximum possible level of 1,259 Vrms. At 32 ohms, it is still a ratio of almost 1:250 with 0.0019 Vrms to 0.4961 Vrms. It is particularly interesting that the values for Vrms are not that far apart.
But what happens when we run the graphics card at full load with maximum FPS? I determine the values with Witcher 3 in the menu and limit the FPS number to 1000 FPS. If you run the game normally with less than 100 FPS, the peak values for Vrms are on the same level, but the frequency of these peaks is lower. Logical. To do this, I set the audio output to zero in the game, so that I again only measure the extraneous noise at the output.
The jumble of curves on the oscilloscope also harmonizes perfectly with the “coil whine” and the power consumption peaks, which clearly points to the graphics card’s voltage converters as the cause. At 0.0151 Vrms, the value at 500 ohms is now over 6 times higher than at idle, resulting in a ratio of just over 1:83. At 32 ohms, it’s still about 5 times what was measured at idle with 0.0095 Vrms, which results in a ratio of 1:49. Here, one then also quickly reaches the perceptible range.
If you’ve been paying close attention, you’ll also notice that the above values coincide with my finding that the setting of the volume control for the speaker/headphone output doesn’t really matter in the absence of a useful signal. One hears these unwanted mixed products unfortunately always!
Therefore, if you connect an analog amplifier, you should always select the distortion-free maximum level on the PC and better turn down the volume on the speaker. This significantly increases the distance between the signal and the interference voltage. This is only cosmetic, but at least helpful.
Intermodulation: Mixed products of a different kind
Don’t be afraid of the bulky term, I’ll explain it to you. Intermodulation (IM) is the creation of new (mixed) frequencies when at least two (or more) different frequencies enter a system with a nonlinear transfer function and are then processed (amplified). On the one hand, we have the audible frequency band of what music or games provide us with, and on the other hand, there are the voltage converters, for example, which clock at about 400 KHz. But not only these.
However, the resulting mixed products are then quickly also in the audible range and you “hear what you see”. The so-called cross modulation is a special form of intermodulation and arises e.g. at nonlinearities of the amplifiers. The higher the quality and shielding of the analog signal path, the lower the levels of these mixed products (“wave salad”). But that’s exactly what you almost always miss with motherboards.
I don’t want to make it too complicated, but I have a nice example of how such a mixed product can negatively affect and even distort our original signal. I first apply a 50 Hz signal at idle and control the amplifier so that the curve is not yet distorted:
The waveform is just perfect and you hear exactly what you expect. How a nicely zoomed out and clean half wave looks, we just had on the previous page.
But what happens when I start the game like I just did? Instead of the gaming sound, I just let the 50 Hz signal continue and record this curve as well. If you look closely, you can see unsightly fringes, especially at the tips of the curves. Unfortunately, they are not the only ones there.
Since it’s hard to see, I’m zooming out another half wave here as well. Only what I see now has nothing to do with a clean 50 Hz curve! Due to the intermodulation this frequency is also influenced and as a product a jittery curve is created! This is annoying, but can no longer be fixed by artifices and tricks.
If the trick with the volume control helped with the signal-to-noise ratio, the distortion of the original signal cannot be eliminated! Even the most expensive DAC doesn’t help, and the most golden capacitors become bored extras when the graphics card hits in such a way. And in Nvidia’s defense, it is fair to say that AMD’s Vega is no less hard to hit and hit again.
Remedy: extra sound card
Let’s first look at the internal solution and install the Creative Sound Blaster X AE5. Let’s now take a look at the 50 Hz curve. This already looks much, much better, but….
… it’s not quite perfect either. But it is quite enough, because who still hears this, may have his ears gilded at state expense.
The fact that the back of the sound card doesn’t have a shielding backplate, but the board is fully in the graphics card’s “radar”, might be disturbing here. The great shield unfortunately points in the direction of the power supply, how convenient! Please think along and improve! We can also see very nicely that we can have a whopping 1.2 Vrms at 32 ohms here when you need it. Running!
A real decoupling can only be achieved at the digital output with an external sound card (USB, SPDIF), which can certainly cost a bit more. I’ll save these curves now, because they are as smooth as a baby’s bottom and thus as you would actually expect them to be. Visual impression see previous page.
Interim summary
If the motherboard is not really one of the extra class, the wheat is separated from the chaff when using a potent graphics card at the latest. You even get the annoying chirping on the desktop when scrolling and the workaround with the adjusted levels only helps against the interference voltages as such, but not against intermodulation products, which unfortunately can also audibly distort the original signals. Of course, everyone will react differently to it and only the practiced or trained ear will normally hear it out. Only beautiful unfortunately goes differently, one way or another.
- 1 - Introduction and general Problems
- 2 - Description: Realtek ALC1220 vs. Realtek ALC1200
- 3 - Description: Realtek ALC4080 and ALC4082
- 4 - Datasheets: Realtek ALC1200, ALC 1220 und ALC 4080 / ALC4082
- 5 - RMS Voltage, Output Power and Sound Pressure Level
- 6 - Graphics cards and Intermodulation
- 7 - Conclusion and final Words
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