What Does It Take To Turn The PC Into A Hi-Fi Audio Platform?

Test Setup: Volume Matching And Testing The Listener

The Listening Environment

All of our tests were conducted in a room with a background noise level of 36.5 dB(A) ±0.2. Of course, we had a PC in the room, and the noise we measured was primarily a result of the system's cooling fans. When my machine dropped to standby, the background noise fell to 32.2 dB(A) ±0.2. In other words, we listened in a very quiet room.

With all of the talk about signal-to-noise (SNR) ratios, total harmonic distortion + noise (THD+N) and dynamic range (DR), it's easy to forget that regular listening environments are inevitably subject to quite a bit of background noise. Beyond a certain threshold, increasingly high SNRs and the "N" component in THD+N become audibly irrelevant when the noise floor of your environment is meaningfully higher than the hardware being tested. That's particularly true for open-back headphones, which, unlike closed-back designs, provide practically no attenuation of ambient noise. Check out some of the (non-scientific) tests in the conclusions page to do a bit of related tests directly on your own.

Imagine trying to listen to your favorite CD on the deck of an aircraft carrier. You can't; the background noise level is so high that you actually need hearing protection. That's an extreme of course, but background noise in any environment still affects what we can hear and what we cannot.

Volume Matching and its Importance

Volume-matching sources when blind listening is important for two reasons. First, if sources are at different levels, they're easy to tell apart. From there, the test is no longer blind. Second, us humans tend to prefer (all other factors being equal) louder sources. Again, that's something we want to control.

It's rudimentary but effective. In this image, we're calibrating headphones using a standard SPL monitor.

Using Sennheiser's HD 800, we accurately volume-matched the individual devices using the 100% digital volume and minimum gain setting of the Asus Xonar Essence STX (which, as an add-in sound card, lacks an analog volume control) and a 1 kHz test tone.

Three test tones at 100 Hz, 1 kHz, and 10 kHz were used from mediacollege.com. The 1 kHz reference level is most important; that's the frequency at which human hearing is most sensitive. The devices we're using are rated to be fully linear in the specified range, so calibration values should match across all three tones.

At 1 kHz, all sound sensor weightings, such as dB(A), dB(C), and dB(Z), are exactly the same with a 0 dB gain. Meanwhile, at 100 Hz and 10 kHz, the weightings yield different values. We're using the common A-weighting, which approximates human hearing best in terms of relative loudness of sounds at different frequencies. This goes a long way in explaining why 100 Hz and, to a lesser extent, 10 kHz, measure consistently lower than 1 kHz. The remaining "drop" comes from the HD 800's own frequency response, which is far from linear above 1 kHz.

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Calibration Tone FrequencyBenchmark DAC2 HGCJDS Labs O2+ODACAsus Xonar Essence STXRealtek ALC889
100 Hz57.0 dB(A) ±0.157.4  dB(A) ±0.156.9 dB(A) ±0.158.3 dB(A) ±0.1
1 kHz93.9 dB(A) ±0.194.0 dB(A) ±0.194.0 dB(A) ±0.193.6 dB(A) ±0.1
10 kHz80.5 dB(A) ±0.181.0 dB(A) ±0.180.3 dB(A) ±0.180.2 dB(A) ±0.1

As you can see, the calibration is very good, though not absolutely perfect. The Benchmark DAC2 is not perfectly aligned because it uses a digital gain control to affect the volume of its digital input. This control has roughly 0.5 dB(A) "steps" at the level we tested, compared to the analog potentiometer in JDS Labs' O2+ODAC. Given the DAC2 HGC's higher price tag, I'm giving it a minor handicap and setting it at the rounded-down closest setting to the other devices. Realtek's codec is slightly softer at 1 kHz and significantly louder (1.4 dB[A]) at 100 Hz. In this sense, it's simply the least-linear or least-transparent of the devices we're testing.

Audiophiles might argue that a listening difference of 0.2 dB is notable, and might impact our test results. This might hold true for a small minority of humans. For us, it does not matter. This isn't just claimed; we'll prove it shortly. Furthermore, 0.2 dB approaches our equipment's margin of error. Realtek's 1.4 dB(A) difference at 100 Hz is the one measurement that might be noticeable.

Of course, listening at >90 dB(A) for extended periods of time can cause hearing loss. You'll be fine a few minutes at a time. But maintaining high volume should be avoided.

The Most Important Instrument to Calibrate: You

Because everyone's ear is morphologically different, we each hear sound uniquely. There are some general truths, though. For example, we become progressively incapable of hearing higher frequencies as we age. The typical human hearing range is conventionally referred to as 20 Hz to 20 kHz (sometimes 22 kHz).

Our tests involve two listeners: a moderate enthusiast, Listener A, accustomed to ~$3000 in audio gear, and a more serious enthusiast, Listener B, used to ~$70,000 in audio gear.

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MeasurementListener AListener B
Highest Frequency Heard17 kHz20 kHz
Lowest Frequency Heard12 Hz14 Hz
Volume Sensitivity (95% Confidence)±1 dB±1 dB

At the high end, Listener A can hear a 17 kHz tone using the DAC2. Tones at 18 kHz and above are absolutely silent. Listener B, despite being a few years older, can hear up to 20 kHz.

On the other end of the spectrum, Listener A can faintly hear 12 Hz. Anything lower is total silence. Listener B's hearing starts roughly at 14 Hz. This is uncommon; typically, the threshold is around 20 Hz. Some say such low frequencies are felt, rather than heard. Another possible explanation is harmonic distortion in the headphones or audio equipment. If that was the case, the tone heard at 12 Hz should sound the same as 24 Hz, but softer. But it doesn't. It sounds far lower than the 24 Hz tone.

Using these calibration settings, a blind A/B test of a difference in ±0.5 dB volume levels at 440 Hz results in a score of 5/10 for both listeners, essentially equivalent to a random guess. That means neither participant can tell 0.5 dB levels apart. To reach a 95% confidence level that listeners can tell volume levels apart, we have to move to ±1 dB, where they score 9/10 or 10/10 consistently.

Thus, the "calibration range" of your listeners today is 12 Hz to 17 kHz and 14 Hz to 20 kHz, with a 1 dB volume sensitivity.

Given that the devices we're testing are calibrated well below the level where either listener can hear the volume difference, we consider them accurately volume-matched (except for Realtek's codec at 100 Hz).

For reference, here is the hardware both listeners use:

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ComponentListener AListener B
Primary source / DACAsus Xonar Essence STX$190Burmester 061 CD Player~€9000
Power conditionerNoneBurmester 038 (no longer in production)~€4000
Integrated amplifierBuilt into powered speakersBurmester 032~€12,000
Secondary power amplifier (For horizontal bi-amping)NoneBurmester 036~€7000
SpeakersYamaha HS80M + HS10W$900Ascendo Z-F3~€21,000
Headphone amplifierBuilt into Asus Xonar Essence STXLehmann Audio Linear SE~€1400
HeadphonesSennheiser HD 800$1500Sennheiser HD 800~€1500
CablesBudget RCA cables$5Burmester/Ascendo cables~€4000

As you can see, Listener A is accustomed to an audio setup worth around $3000. Listener B is in another category altogether, with a configuration well into five figures. Listener A's setup is also a 2.1-channel near-field active-monitor setup, while Listener B's setup relies on high-end full-range speakers. Both listeners are well-acquainted with Sennheiser's HD 800 headphones though, which are what we'll primarily be using for our tests.

  • SuckRaven
    Bravo ! Awesome, and a very thorough review. Even though as you mention, audio gear is not usually the forté/emphasis of the reviews here, it's refreshing to have someone at least try to cut through the (more often-than-not) overpriced arena of bullshit that is the field of "high-end" audio. I applaud the review, and the effort. Keep up the good work. More please.
  • PudgyChicken
    Just wondering, why not test a Creative X-Fi Titanium HD or something like that alongside the ASUS Xonar? It would be interesting to see some of the differences between different PCIe sound cards in this matchup. However I understand that what you were really going for was showing the difference between price point and form factor at the same time, so perhaps not testing two PCIe cards makes sense.
  • kitsunestarwind
    The biggest thing I have found for the PC is no matter how good your DAC is , if your speakers and AMP are crap, then it will never sound better.People spend big money on DAC's and forget that you need a high Quality amp with very very low THD (total harmonic distortions) and a very good set of Full Range speakers with high sensitivity if you want good sound, instead of crappy (albeit expensive) computer speakers especially sets with a sub.
  • shahrooz
    this article just won Tom's Hardware Readers Elite award
  • maestro0428
    Wonderful article! I love listening to music and do so mostly at my PCs. I try to set up systems where audio is important in component selection. Although we all love drooling over expensive equipment, many times it is not all that necessary for an amazing experience. I'd love to see more! Including smaller, studio speakers as I believe that speakers/headphones are the most important part of the equation. Keep up the great work!
  • blackmagnum
    Don't forget that for PCs: the hardware is as good as its software (drivers).
  • Someone Somewhere
    Agree totally with this. It always annoys me when people say they're spending over $100 on a sound card, especially when it turns out that they're using Optical out, and the whole thing is basically moot.I now have a nice source to link to.
  • 1zacster
    The thing is you can't just pick up two sets of good headphones, try them on different DACs/AMPs and expect to hear major differences, it takes longer than 5 minutes for your ears to adjust to newer headphones and for the differences to actually show. This is like taking food from Left Bank and then bringing in a bunch of hobos and asking them tel tell the differences between the foods.
  • dogman-x
    I use an optical cable from my PC to a home theatre receiver. With this setup, stereo CD audio content is sent as raw PCM to the receiver, not compressed into DD or DTS. These days you can buy a very good quality home theatre receiver for less than $200. Audio quality is outstanding.
  • Memnarchon
    I would love to see ALC1150 in these tests too, since its widely used at most Z87 mobos.