USB Audio,USB audio chip,Voice command,Sound technology--C-Media Electronics, Inc.

In USB Audio, the Host (computer) and Device (DAC/Headphones) use independent oscillators, making perfect clock sync difficult. To avoid Buffer Overflow or Underflow (which causes audio glitches), the USB spec defines three Synchronization Types:

1. Synchronous Mode: Standard for basic USB audio devices

How it works: The device's clock is locked to the USB bus. It adjusts its sampling rate to match the host's transmission speed.
Pros: Simple design and low cost.
Cons: Highly susceptible to USB bus jitter, resulting in mediocre sound quality.

2. Asynchronous Mode : the standard for high-end audio (Hi-Fi DACs)

How it works: The device uses its own high-precision clock and dictates the data rate to the host via a "Feedback Endpoint."
Pros: Eliminates USB host jitter for the purest sound.
Cons: Higher hardware cost and complex firmware development.

3. Adaptive Mode: A middle-ground solution

How it works: The device adapts to the host’s data stream. It uses a VCXO (Voltage-Controlled Crystal Oscillator) to dynamically adjust its internal sampling rate to match the host.
Pros: More stable than Synchronous mode; no feedback mechanism required.
Cons: Still limited by host clock quality; more complex circuit design than Synchronous.

Comparison	Synchronous	Adaptive	Asynchronous
Sync Mechanism	Locked to USB Bus (SOF Signal)	Internal (Follows Host Rate)	Internal (Independent High-Precision Clock)
Control by	Host-Driven	Device Passively Adapts to Host Rate	Device-Driven (via Feedback Control)
Jitter	Highest (Strongly affected by USB Bus)	Medium (Affected by Host Clock)	Lowest (Determined by Device Hardware)
Audio Performance	Poor (Prone to noise floor or harshness)	Fair to Good	Superior (Hi-Fi Standard)
Hardware Requirements	Extremely Low	Moderate (Requires clock adjusting circuitry)	High (Requires Precision Clock and Independent Oscillators)
Firmware Complexity	Simple	Moderate	Complex (Requires Feedback Mechanism)
Applications	Budget Toys, Telephony Headsets	Legacy Sound Cards, General Computer Peripherals	High-End DACs, Professional Recording Interfaces

C-Media IC Sync Mode Comparison

Sync Mode	Application	Representative IC
Asynchronous	High-Fidelity (Hi-Fi), Gaming, and Hi-Res Products	CM6635, CM6542
Adaptive	Entry-Level & Standard Universal Products	CM108B, HS-100B
Synchronous	Legacy or Specialized Industrial Applications	NA

Cmedia’s privacy policy covers the collection and use of personal information that may be collected by Cmedia anytime you interact with Cmedia, such as when you visit our website, when you purchase Cmedia products and services, or when you contact our sales or support associates. Please take a moment to read the following to learn more about our information practices, including what type of information is gathered, how the information is used and for what purposes, to whom we disclose the information, and how we safeguard your personal information. Your privacy is a priority at Cmedia, and we go to great lengths to protect it.

Why do we collect your personal information? Because it helps us deliver a superior level of customer service. It enables us to give you convenient access to our products and services and focus on categories of greatest interest to you. In addition, your personal information helps us keep you posted on the latest product announcements, software updates, special offers, and events that you might like to hear about.

There are a number of situations in which your personal information may help us give you better service. For example, we may ask for your personal information when you’re discussing a service issue on the phone with an associate, downloading a software update, registering for a seminar, participating in an online survey, registering your products, or purchasing a product. At such times, we may collect personal information relevant to the situation, such as your name, mailing address, phone number, email address, and contact preferences; your credit card information and information about the Cmedia products you own, such as their serial numbers, and date of purchase; and information relating to a support or service issue. We collect information for market research purposes, such as your occupation and where you use your computer, to gain a better understanding of our customers and thus provide more valuable service. We also collect information regarding customer activities on our website, and on related websites. This helps us to determine how best to provide useful information to customers and to understand which parts of our websites and services are of most interest to them.
If you use a bulletin board or chat room on a Cmedia website you should be aware that any information you share is visible to other users. Personally identifiable information you submit to one of these forums can be read, collected, or used by other individuals to send you unsolicited messages. Cmedia is not responsible for the personally identifiable information you choose to submit in these forums.

Cmedia takes your privacy very seriously. Be assured that Cmedia does not sell or rent your contact information to other marketers. To help us provide superior service, your personal information may be shared with legal entities within the Cmedia group globally who will safeguard it in accordance with Cmedia’s privacy policy. There are also times when it may be advantageous for Cmedia to make certain personal information about you available to companies that Cmedia has a strategic relationship with or that perform work for Cmedia to provide products and services to you on our behalf. These companies may help us process information, extend credit, fulfill customer orders, deliver products to you, manage and enhance customer data, provide customer service, assess your interest in our products and services, or conduct customer research or satisfaction surveys. These companies are also obligated to protect your personal information in accordance with Cmedia’s policies. Without such information being made available, it would be difficult for you to purchase products, have products delivered to you, receive customer service, provide us feedback to improve our products and services, or access certain services, offers, and content on the Cmedia website.
At times we may be required by law or litigation to disclose your personal information. We may also disclose information about you if we determine that for national security, law enforcement, or other issues of public importance, disclosure is necessary.

Cmedia takes precautions, including administrative, technical, and physical measures, to safeguard your personal information against loss, theft, and misuse, as well as unauthorized access, disclosure, alteration, and destruction.
You can help us by also taking precautions to protect your personal data when you are on the Internet. Change your passwords often using a combination of letters and numbers, and keep them confidential. If you are sharing a computer with anyone, you should always choose to log out before leaving a site or service to protect access to your information from subsequent users.

Cmedia has safeguards in place to keep your personal information accurate, complete, and up to date for the purposes for which it is used. You can request a copy of your personal information, and your interactions with our sales and support agents by contacting us at the email address below.

As is standard practice on many corporate websites, Cmedia's website uses cookies and other technologies to help us understand which parts of our websites are the most popular, where our visitors are going, and how much time they spend there. We also use cookies and other technologies to make sure that our online advertising is bringing customers to our products and services. We use cookies and other technologies to study traffic patterns on our website, to make it even more rewarding as well as to study the effectiveness of our customer communications. And we use cookies to customize your experience and provide greater convenience each time you interact with us.
For example, knowing your email address allows us to send you informative newsletters and driver information, and generally helps us provide a more useful online experience.

If, however, you prefer not to enable cookies, please go to www.CMedia.com/legal/privacy/about_cookies.html, which explains step by step how you can disable cookies. Please note that certain features of the Cmedia website will not be available once cookies are disabled.
As is true of most web sites, we gather certain information automatically and store it in log files. This information includes internet protocol (IP) addresses, browser type, internet service provider (ISP), referring/exit pages, operating system, date/time stamp, and clickstream data. We use this information, which does not identify individual users, to analyze trends, to administer the site, to track users movements around the site and to gather demographic information about our user base as a whole. Cmedia will not use the information collected to market directly to that person. In some of our email messages we use a lick-through URL linked to content on the Cmedia website. When a customer clicks one of these URLs, they pass through our web server before arriving at the destination web page. We track this click-through data to help us determine interest in particular topics and measure the effectiveness of our customer communications. If you prefer not to be tracked simply avoid clicking text or graphic links in the email. In addition we use pixel tags tiny graphic images to tell us what parts of our website customers have visited or to measure the effectiveness of searches customers perform on our site.
Pixel tags also enable us to send email messages in a format customers can read. And they tell us whether emails have been opened to assure that we only sending messages that are of interest to our customers. We store all of this information in a secure database located in Canada.

To make sure your personal information is secure, we communicate these guidelines to Cmedia employees and strictly enforce privacy safeguards within the company. We do not knowingly solicit personal information from minors or send them requests for personal information.
Cmedia website has links to the sites of other companies. Cmedia is not responsible for their privacy practices. We encourage you to learn about the privacy policies of those companies.

If you have questions or concerns about Cmedia Customer Privacy Policy or data processing, please contact us at privacy@cmedia.com. If you do not want Cmedia to keep you up to date with Cmedia news, software updates and latest information on products and services, click the "unsubscribe" link that is included in the email sent. Naturally, if you notify us that you do not want us to use your information for a particular purpose, we will not do so.
Cmedia may update its privacy policy from time to time. When we change the policy in a material way a notice will be posted on our website along with the updated privacy policy.
This policy last updated 16 March 2006.

This website and its contents are c Copyright Cmedia Electronics Inc. All rights reserved. Cmedia Electronics Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damage caused, or alleged to be caused, directly or indirectly by the information contained within this website.
When you access/browse/use this site you agree to the terms and conditions stated herein.

The content of this website is meant for the sole purpose of providing information about Cmedia products. All contents of this website, including, but not limited to text, illustrations, photographs, sound files, animation files, video files, icons, interfaces and layouts or other such arrangements are the copyrighted property of Cmedia Electronics Inc. or have been licensed from the copyright owner for use on this site and may not be used for any purpose whatsoever without our express written permission. Such permission is automatically granted to Authorized Layton Electronics and Networking Limited Dealers and their authorized agents only subject to the Terms and Conditions of our Authorized Dealer/Affiliate Agreement(s). Any unauthorized use of the content of the website by any other party will violate various copyright laws, trademark laws, the laws of privacy and publicity, and civil and criminal statutes.

This website may not be linked to or linked from any external website without our express written permission. Authorized Cmedia Electronics Inc. Dealers may link to the Home Page only of this site subject to the Terms and Conditions of our Authorized Dealer/Affiliate Agreement(s).

The information provided within this website is supplied "as is" and without warranty of any kind, expressed or implied, including but not limited to any implied warranties of merchantability, fitness for any particular purpose, or non-infringement. E&OE.

Cmedia Electronics Inc. reserves the right to change specifications, features and/or prices without notice.

The wordmarks, service marks, trademarks and associated tag lines used within this site are the exclusive property of Cmedia Electronics Inc. All rights reserved. They include but are not limited to the following:

Cmedia Electronics
Cmedia “C” logo
Cmedia Hydrogen
Wi-Sonic
Cmedia Oxygen and Cmedia Oxygen HD

USB Audio: Three Synchronization Types