Improving your PC's stereo playback on a budget February 23, 2006

Introduction

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In a survey we conducted last September, we discovered that about half of FiringSquad readers use a 2-channel audio setup (headphone or speakers) and half of you use a multi-channel system. These findings aren’t surprising. While multi-channel audio is important for games and movies, MP3s and WMAs are stereo. It turns out that the best sound card for multi-channel games usually isn’t the best sound card for music. The problem is that most sound cards operate at a native 48 kHz sampling rate. This means that for every second of sound, there are 48,000 slices of the waveform. As you can imagine, the smaller the slices, the more accurate the recording will be. Games, sound effects, and DVDs all use a 48 kHz sampling rate. On the other hand, most PC music is recorded at 44.1 kHz – that’s what music CDs are recorded at.

The problem arises when you have to convert the 44.1 kHz data for a 48 kHz sound card. Since the samples aren’t evenly divisible (i.e. converting 22.05 kHz to 44.1 kHz), the conversion process usually introduces artifacts that diminish sound quality. Therefore, even if you run the digital output of your motherboard’s sound card to a high-end receiver, you’re still dealing with the 44.1 khz to 48 kHz conversion. One approach to solving this translation problem is through sophisticated algorithms. The X-Fi dedicates 7310 MIPS of processing power just for conversion of 44.1 kHz audio to 48 kHz data. However, there’s an easier and cheaper way to add 44.1 kHz audio support to your motherboard. It’s called the VIA Envy24.

VIA Envy 24HT

The Envy24HT is great because it provides a dirt cheap solution to high-end audio. For less than $25, you get true 16-bit/44.1kHz audio, important for MP3 and CD audios, but also 24-bit/96kHz playback support. Since the design of the sound card is exceptionally simple, manufacturers are still able to include high-end DACs without increasing the cost. Best of all, the Envy24HT “plays nice” as a second sound card. This makes it a great add-on to your motherboard sound card or even another PCI sound card.

If audio fidelity during music CD or MP3 play back is important to you, the Envy24 HT is unquestionably the best starting point.

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Moving On Up

Before I tell you about the options, it’s important to look at the weakest links of the Envy24: the DACs and the OP-AMPs. While the DAC better than most PC sound cards, this is the one component where there is sufficient room to grow. The DAC plays the crucial role of translating the 1’s and 0’s of the audio signal into the analog domain. It’s responsible for reconstructing the audio waveform. The OP-AMP is the low-power amplifier that takes the output of the DAC and amplifies the signal so that it’s usable with you headphone. Since these components are on the sound card and the inside of the PC is an “electrically noisy” environment due to all the fans and EMI, noise and distortion get introduced into the audio signal. The noise and distortion are minimal, but it can be a problem if your speakers or headphones are good enough to resolve the details. Therefore, the trick is to move the DACs and OP-AMPs outside of the computer. There are two different approaches to take.

S/PDIF

The most common approach is to use the optical or coaxial digital output of the sound card. By routing the signal to your expensive surround sound receiver, you get to rely on the (usually) higher-end DACs and OP-AMPs in that machine. When the Envy24’s first came out, I would have told you that you’d need to spend $500+ on a receiver to get one that was substantially better than the on-board sound. Now, with most receivers under $500 using digital amplification technology, using the S/PDIF connection is a reliable approach. The problem is that you do need to have a full-sized receiver as part of your PC setup. For some people this works perfectly, and for others it doesn’t work at all.

USB External Sound Cards

The second option is to go with an external USB sound card. In this case, the idea is that you can move the entire sound card outside of the PC environment. We tried this before with the Audiophile USB in 2003. Unfortunately, consumer-grade external USB sound cards never seemed to work as well. Turns out that the problem was jitter.

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For some people, jitter is a voodoo science of hi-fi digital audio. Bits are bits right? Perfect sound forever? It turns out it’s not that simple.

How would you pronounce “cho pho use?" Think about it for a while. Sound it out.

What if I wrote it as “chop house?”

All I’ve done is change the timing in which the data has come to you. When it comes to audio, a DAC expects data to come every 1/44100 seconds. If the data comes in a fraction of a second too early, the sound card buffer can overfill. If the data comes in a fraction of a second too late, the DAC has to “guess” at what kind of data it needs to send out. This corrupts the audio resulting in worse fidelity.

USB is a high-jitter interface

Although a USB sound card helps you move the circuitry away from the noisy environment inside a PC, the USB interface itself has a substantial amount of jitter. USB has four different transmission modes. Two of those are designed for transferring a large amount of data.
1) Isochronous mode. A fixed number of packets are sent and received.
2) Bulk mode. A fixed quantity of data is sent each time. If data is lost, it’s resent.

Bulk mode works well for hard drives and printers because errors can be corrected through retransmission. For audio data, retransmission wouldn’t work because the delay would cause the music to stutter. So for audio, you have to use the isochronous mode where there’s no re-sending of packets.


In the end, USB sound cards end up being a wash. The benefits from moving the sound card out of the machine are cancelled out by distortion that gets added from the USB circuitry.

Burr Brown Japan’s solution

The engineers at Burr-Brown Japan came up with a better way: a feed-forward tracking PLL. Essentially, a very high-speed tracking system in which the transmitting frequency is determined by calculating the differences between two packets. The chip was the PCM2702.

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Hands on Testing

SilverStone provided an EB01 to us for review. The EB01 is SilverStone’s first product in their Ensemble audio line and retails for about $100. What makes it special is that SilverStone took a purist’s approach to audio. Rather than just trying to focus on specs and selling a “24-bit / 96 kHz” sound card which may offer compromised performance, SilverStone chose to go with the Burr Brown PCM2702 chip given its ultra-low jitter performance. The PCB is a 4-layer design with a standard OPA624 op-amp. Although the OPA624 is considered a “run-of-the-mill” operational amplifier with a slew rate is 25 V/microsec (how fast it can change the signal) versus the OPA627’s 55V/microsec, it’s still substantially better than the typical 5V/microsec performance of the conventional op-amps in your typical sound card.

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Conclusion

When FiringSquad started, gamers were debating between the SB Live! and the Monster Sound MX300. Now, it doesn’t really matter whether the onboard soundcard has a C-Media, Realtek, or Analog Devices CODEC. For the majority of PC enthusiasts, the on-board sound card offers more than enough performance. It’s clearly the best bang-for-the-buck, because it’s free. However, if you use your PC for music playback, upgrading to the Envy 24 is an obvious first step. Whether you’re interested in using it for analog playback or even 44.1 kHz S/PDIF output, it’s hard to find a better PCI sound card for the money. It sounds essentially as good as a mid-range X-Fi, but comes at a price advantage. For the small group of you who want even better audio quality than the Envy24 has to offer for your music, your best option comes from one of two solutions: 1) Using the Envy24 SPDIF to a high-end receiver or 2) Using the an external USB soundcard powered by a chip such as the Burr Brown PCM2702.