Computer Audio Misconceptions
If you’ve been involved in computer audio for any amount of time, you’ve likely heard all sorts of conflicting opinions. Over the years, I’ve heard customers make statements like these:
- “Computers use error correction, so upgrading the power supply makes no difference.”
- “If the USB input on the DAC is asynchronous, all the jitter and bit read errors are removed.”
- “If the output from the computer is reclocked, all the jitter and bit read errors are removed.”
- “If the player software buffers to RAM, everything output from the computer is bit perfect.”
- “Batteries have pure DC power, which makes them optimal for any type of digital circuit.”
Though there is some basis in fact for all of the above statements, they are all somewhat incomplete and/or conditional. I wrote this blog to clarify these common misconceptions. To make the information more accessible for readers who are not computer geeks, I’ve generalized my responses somewhat. My intention is to help readers to understand technology so that they can have the best-sounding systems possible. So please accept my blog in that spirit. I welcome readers to send constructive criticisms that could be used to improve both the content and the way it is communicated.
Before going any further, I need to define the term "bit perfect" as it is used in the blog so as to not confuse my readers. The term "bit perfect" is a technical term that is used to describe any form of digital communication that involves a series of checks and error correction (i.e., checksum), ensuring the data that arrives at the receiver is identical to the data that was transmitted from the source. This is what allows you to download a file from a server halfway around the world and know that it will arrive at your computer identical in every way to the original.
The term "bit perfect" was adopted by the audiophile industry and used to describe music player software that accurately represents the quantized values of the original music data that it reads from a storage device and transfers out of the computer's communication ports. There is no resampling, digital signal processing (DSP), attenuation, or interpolation. When the term "bit perfect" is used in regards to player software, it can be somewhat misleading since it implies that what is output from the computer has not been altered in any way from the original music data file. If this were true, then all so-called "bit perfect players" would sound identical, and this is certainly not the case. What would be more accurate would be to say that a specific music player software can be operated in "bit perfect mode," in which no algorithms were purposely used to alter the original data file.
As with many other things in the "audiophile" market, so-called "bit perfect" player software does not always live up to its name. In a future blog, I'll be discussing the topic of music player software, but for the time being, I recommend you view the claims of companies that sell music player software as "marketing language" as opposed to quantifiable facts.
Please keep in mind that this blog attempts to convey technical concepts in layman's terms, and every reader might not agree with our geek-to-English translations. If you want clarification on any of the points made in this blog or more information about any of the topics covered, please feel free to contact me directly.
How can a low-noise power supply improve computer performance?
Most computer communication works on a system of checks and error correction. If a packet of data doesn’t pass the check at the receiver, a new packet of data is requested and sent to replace the original.
A computer that has less power supply noise will make fewer bit read errors, so the computer will have fewer errors to correct. This frees up system resources and allows packets of data to be transmitted and buffered in a more sequential order, which translates to less jitter. The lower the noise in a computer’s power supply, the more harmonically coherent, the more liquid, and the more articulate the sound.
Aren’t RAM-buffered music players bit perfect?
When music data is buffered to RAM by the player software, the data in the RAM is bit perfect, but RAM is not the final link in the chain. Bit read errors can still occur between the RAM and the output buffer, and between the output buffer and the digital to analog converter (DAC). Bit read errors that occur between RAM and the output of the computer are error corrected by the operating system's data transmission protocols, but this will use system resources that potentially results in more jitter. Unlike most other computer communication, the music data that is output from a computer through USB, Firewire, and optical ports is most often done using a unidirectional protocol and is not error corrected when it arrives at the DAC.
Doesn’t reclocking data from the computer eliminate jitter and bit read errors?
Reclocking and/or buffering music data can remove jitter and will improve performance by minimizing bit read errors, removing digital noise, cleaning up the square wave of the digital signal, and buffering enough clock cycles so as to allow all of the bits in each digital word to be read within the appropriate clock cycle. This process minimizes bit read errors in subsequent stages, but it doesn't correct existing corrupted data. If corrupted data exists, unless the reclocking and buffering device has a bidirectional protocol that incorporates error correction, these bad bits will continue through to the next stage.
Aren’t streaming devices bit perfect?
Streaming devices receive data wirelessly from a computer in a local area network. This means they use the same checking and error-correcting protocols as other Wi-Fi devices, which ensures that uncorrupted bit perfect data is received. The problem with most of these devices is that they have limited resources; they don’t have nearly as much processing power or RAM as an actual computer. Fewer system resources means more jitter, which translates to a less harmonically coherent, less liquid, and less analog-like sound.
Of course, many of the popular streaming devices use cheap wall wart type switching mode power supplies (SMPS), which cause significantly more corrupted data in the output stage. This is why replacing a wall wart SMPS with a battery or linear power supply will significantly improve the performance of these components.
Don’t asynchronous USB inputs remove all jitter, resulting in bit perfect sound?
Asynchronous communication is defined as transmission of data without the use of an external clock signal. This allows data to be transmitted intermittently rather than in a steady stream. This also allows for variable bit rates and eliminates the need for the transmitter and receiver to have their clock generators synchronized.
Asynchronous digital communication is nothing new. It has been used for decades in obsolete protocols, such as RS-232C. Adopting it for USB audio inputs was one of several potential data transmission protocols and is far from what would be considered cutting edge technology.
As stated earlier, most computer communication is bidirectional and works with a system of checks and error correction. When the source sends a packet of data, the destination checks the packet and requests corrupted data packets to be resent. Since the asynchronous USB protocols used for most audio data is unidirectional, when an error occurs, no resend or error correction is possible.
The combination of asynchronous clocking and data buffering can remove jitter caused by packets of data arriving at irregular intervals, but it can’t correct corrupted data. Though asynchronous USB results in smoother and more analog-like sound, if it isn't bidirectional it has no error correction and can not assure uncorrupted bit perfect data.
Don’t batteries have the purest DC power?
There’s a common misconception that batteries have the purest DC power. Though batteries are better than the inexpensive wall wart type switching mode power supplies (SMPS) that come with many audio, video, and computer products, battery performance can’t compare to the performance of an ultralow-noise linear power supply.
Batteries use a chemical reaction to generate DC power, and each chemical reaction from each type of battery has its own audible noise signature. That’s why a specific type of battery, such as LIO4, sounds better than another type, such as SLA. In addition, the noise level of a battery changes significantly during different phases of the recharge cycle, making batteries an inconsistent-sounding power source. Of course, batteries also wear out and need replacing every year or three, which adds significantly to the cost of ownership.
Though superior to nearly any other digital source that can be used to reproduce recorded music, computer-based music server technology is still in its infancy. Many of the so-called “cutting edge” protocols are obsolete, and many of the so-called “breakthrough” interface devices are mere band aids that attempt to correct unnecessary data corruption that inevitably comes when manufacturers bow to market demand and produce smaller, more affordable, and more energy- efficient products that appeal to the mass market versus the uncompromising audiophile consumer.
USB, Firewire, and Thunderbolt ports were engineered for convenience, satisfying the “plug and play” requirements of the technically unsophisticated mass-market consumer. With power and signal intimately contained within a single cable, these products were never intended to be no-compromise data transfer mediums.
A simple way to prove or disprove the bit perfect status of a computer-based audio system (note the term "system" and not "software") is to compare a $10 digital cable with an expensive audiophile cable. If you can hear any difference between these two cables, you can be certain that the system does not employ error correction in its final stage(s) and is not delivering uncorrupted bit perfect data to your DAC. If the digital input device on a DAC error corrects corrupted data a $10 digital cable would sound nearly identical to the best audiophile digital cable in the world.
Many of the better pro audio ADC/DAC systems have a board inside the computer that interfaces with an external component. Often the purpose of this board + external ADC/DAC topology is to incorporate an error correcting protocol and assure uncorrupted bit perfect data transmission in and out of the computer.
The shortcomings of market-driven technology have also affected power supplies and integrated circuit topology. Since the SMPS used in most computer and media devices are significantly smaller, cheaper, and more energy efficient than ultralow-noise linear power supplies, and since fast integrated circuits and error-correcting protocols are less expensive to implement than error prevention, most modern digital devices use processor speed and other system resources as an economical, energy-efficient, and space-saving alternative.
The most significant way to circumvent the shortcomings of mass-market computer products is to minimize power supply noise. When power supply noise is minimized, the result is cleaner and more defined “square waves” in the digital signal, which translates to fewer bit read errors, less error correction, and less jitter.
Would you like to prove or disprove this for yourself?
One way to prove or disprove how much power supply noise can effect computer audio performance is to use an AC power conditioner. If you can hear any improvement in system performance using an AC power conditioner, then you can be certain power supply noise was corrupting your data.
Another inexpensive way to prove or disprove the effect power supply can have on computer audio is to replace the wall wart or SMPS on your computer or digital device with an LIO4 battery or linear power supply. If you can hear any improvement in system performance when you switch the SMPS to a battery or linear power supply, you can be certain that power supply noise was corrupting your data.
For even higher performance, you could audition one of Mojo Audio’s ultralow-noise power supplies or media servers. Of course, one advantage of going with Mojo Audio's products is that with our 45-day no-risk audition, you have nothing to lose but your misconceptions.
I will soon be posting a new blog that will give step-by-step instructions on how to upgrade the power supply in a Mac Mini. The guide will outline several options, including bypassing the internal SMPS to use an external battery or a bench-type low-noise linear power supply, as well as detailed instructions on how to do a DIY upgrade using components from Mojo Audio.
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