USB and Ethernet audio

Over the last decade the way we find, store, and listen to music has undergone a huge change. Online media has changed many aspects of the audio industry, but some things just don’t change. The debate over audio quality still goes on. Ethernet AVB, USB Audio Class 2.0 aid audio quality article discusses on some facets of audio quality and how they relate to USB and Ethernet. It has few points really worth to share.

CDs are sampled at 44.1 kHz using 16-bit samples. Most pro audio equipment now supports sample rates of 96 kHz, and some even support 192 kHz. High-quality audio probably demands data rates of at least 128 kbits/s in AAC forma (AAC at 256 kbits/s is the default encoding used by Apple iTunes). There are a number of other audio codec “standards” around, including FLAC (Free Lossless Audio Codec).

According to Ethernet AVB, USB Audio Class 2.0 aid audio quality article USB is ubiquitous and well suited to audio. USB 2.0 High Speed and USB Audio Class 2.0 (a driver for any USB 2.0 port) include a number of features to ensure the audio is transferred reliably and with high quality: USB Audio Class 2.0 enables 192-kHz, and even 384-kHz, 24-bit audio, and many audio channels. It allows also low latency and asynchronous clocking of D/A converters. Articles USB audio simplified and USB-to-I2S audio bridge chip simplifies audio design give some more details on USB audio.

The interest in audio over Ethernet is increasing. Ethernet AVB, USB Audio Class 2.0 aid audio quality article mentions that in live sound and professional applications Ethernet has found a place to distribute audio signals. Ethernet Audio Video Bridging addresses this problem related to reliably transporting audio by providing reliable transport of audio across Ethernet networks. AVB is a collection of IEEE standards which augment Ethernet to provide functionality needed for AV distribution in professional and consumer applications, and is even finding its way into automotive.

Many other audio over Ethernet solutions also exist and are used. From them first comes to my mind are CobraNet (first commercially successful implementation of audio over Ethernet), RockNet and NetJack. Audio over Ethernet is a nowadays a viable alternative to analog audio, which suffers from signal degradation over long cable runs due to electromagnetic interference, high-frequency attenuation, and voltage drop. Additionally, the use of digital multiplexing allows audio to be transmitted using much less cabling than analog audio.

10 Comments

  1. Tomi Engdahl says:

    Select your USB audio MCU with care: Scary stories from the test bench
    http://www.edn.com/design/consumer/4419643/Select-your-USB-audio-MCU-with-care–Scary-stories-from-the-test-bench

    USB audio is alive and well, and reports of its demise at the hands of wireless transports such as Wifi and Bluetooth are premature. It has recently become an especially important factor in digital audio (and audio+MIDI) accessories for the music industry (mixers, DJ equipment, digital audio interfaces, microphones, etc.).

    More and more, powerful mobile devices are replacing laptops and portable computers, as highlighted in this USA Today article. And the need for USB audio doesn’t stop at professionals or ‘prosumer’ users, as it’s now readily accessible on many mobile OSs such as iOS and Android, and on hobbyist/maker SBCs such as the Raspberry Pi and BeagleBone Black.

    It’s a low-cost, low-power approach to the transport of digital audio and, at its best, can deliver a combination of high quality and low latency that the common wireless methods can’t match. But there’s the rub – you need to make sure it’s working at its best!

    The key problem that needs to be solved when replaying (or recording) high-quality audio through a USB interface is the generation of the necessary converter master clocks to a very high degree of stability and accuracy. Shortcomings in the audio clock recovery process caused by insufficient attention to detail at the design stage can easily result in measurable imperfections and clearly audible nuisance even to the average consumer.

    Reply
  2. Tomi Engdahl says:

    Building a ‘high-end’ USB audio DAC
    http://hackaday.com/2013/08/27/building-a-high-end-usb-audio-dac/

    As [Jan-Erik] had already built a simple USB connected Digital-to-Analog Converter (DAC), he decided to make the high-end version of it.

    JEDAC – yet another take on a DIY high-end USB Audio DAC
    http://users.abo.fi/jskata/JEDAC/

    If you are wondering what an Audio DAC is, this might not be the project page you are looking for.
    But for short, a DAC (Digital-Analog Converter) is a computer soundcard, in this case intended to give the maximal (audiophile) audio quality in terms of reconstruction accuracy, signal/noise level and channel separation.

    Having previously built a simple USB DAC with PCM2705, I was surprised by the improvement in sound quality over the motherboard sound output.

    I decided to go full out and build a more ambitious DAC using PCM2707 (PCM2705 is NRND and the TQFP32 of PCM2707 is better to hand solder compared to SSOP28).
    This will also be entirely USB powered, like it or not.

    Reply
  3. Tomi Engdahl says:

    Can You Hear the Difference?
    http://www.edn.com/electronics-blogs/rowe-s-and-columns/4421042/Can-You-Hear-the-Difference-

    It’s not unusual to use USB to carry digitized audio. After all, even USB 1.1 has the bandwidth. You may have USB speakers or you may stream audio from a hard drive that’s connected to your computer through a USB cable. Can you hear the distortion that the USB link adds to your music? Some people think they can.

    One of our bloggers just sent me a link that, as connections go, is absolutely hilarious. The Absolute Sound, a site for audiophiles, posted its 2013 TAS Editors’ Choice Awards: Digital Interconnects. Let’s start with the first one.

    AudioQuest Diamond
    0.75m, $549; 1.5m, $695

    Deep musical involvement? We’re talking a digital cable here. Audiophiles, please get your ears out of the sand and listen to me. USB is a digital bus. As long as the receiver can properly receive the bits and tell the difference between a logic 1 and a logic 0, the digital representation of the audio at the receiver’s output will be a perfect replica of that which was transmitted.

    You claim that you can hear the difference between an inexpensive and expensive USB cable? I’m sorry, but you have been deceived. On average, digital links deliver one bit error for every 1012 bits sent. You can’t possibly hear that. Next, you’ll tell me that you can hear the difference in clock jitter produced by that inexpensive cable. Again, as long as the bits are properly interpreted, there is no difference in signal as a result of a cable.

    If there is any distortion in the entire audio chain, it’s on the analog side.

    Now, I can understand not buying the cheapest of USB cables, but I’d do that for reliability, not audio quality.

    Don’t fool yourself. Paying $695 for a USB cable will not get you better audio. You will get the same audio quality from a $6.95 cable. The audio quality is a function of the original encoding, the decoding, the analog signal processing and amplifier, and the speaker. Go ahead, prove me wrong.

    Reply
  4. Zoila says:

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    Reply
  5. AVB, Audinate Dante, and AES-67 « Tomi Engdahl’s ePanorama blog says:

    [...] AVB, Audinate Dante, and AES-67 The trend in professional audio systems seems to be that audio signals are move and more moving from balanced analogue interfaces and proprietary digital interfaces to Ethernet networking. There are many good reasons for that, which I am not going through in this post, for more information on reasons for transition look my earlier postings Dante and AVB and USB and Ethernet audio. [...]

    Reply
  6. Tomi Engdahl says:

    Bringing Plug-and-Play Simplicity to Your Next Audio Design with the CP2615 USB-to-I2S-Bridge
    http://community.silabs.com/t5/Official-Blog-of-Silicon-Labs/Bringing-Plug-and-Play-Simplicity-to-Your-Next-Audio-Design-with/ba-p/196017?utm_source=newsletter&utm_medium=email&utm_campaign=april2017newsletter&mkt_tok=eyJpIjoiTWpFeU5HVmhaREJrT0dFMyIsInQiOiJnWWlqaVc2OVJkMnhYb3ZGVGMzZVJUOWtMdVBJSU41czJ6XC9nRk1aZjB6eFp1WWNxR3dxUjlYbk9OUk9TbnFiMXhhSmhKQ0RaSWY1ZStOZ2RzVFdSaEFseUs2Ryt4eEZvUmQwNllnbjlHQXprZXhaZXhib3RFYWdESVFtWXRSZ1kifQ%3D%3D

    Looking to develop a new USB audio accessory? Need to get that to market quickly? No worries. We’ve got you covered. USB system development often involves significant protocol expertise, design effort, and cost for proper implementation. Additionally, USB audio development requires sophisticated clock synchronization which poses further development challenges. To address these needs, and to get your products to market faster, we’re introducing a highly integrated fixed-function USB-to-I2S bridge device, the CP2615.

    The CP2615 USB-to-I2S bridge device is designed for rapid development of USB-based audio applications such as USB headphones, headsets, speakers, and other accessories. These devices simplify the process of transferring audio data from USB to I2S without the need for any complex protocol expertise or time consuming code development. The CP2615 includes a USB 2.0 full-speed function controller, USB transceiver, oscillator, I2S (audio) interface and I2C (control) interface in a compact 5×5 mm QFN32 package ideal for space constrained applications.

    Reply
  7. Tomi Engdahl says:

    Select your USB audio MCU with care: Scary stories from the test bench
    http://www.edn.com/design/consumer/4419643/Select-your-USB-audio-MCU-with-care–Scary-stories-from-the-test-bench

    USB audio is alive and well, and reports of its demise at the hands of wireless transports such as Wifi and Bluetooth are premature. It has recently become an especially important factor in digital audio (and audio+MIDI) accessories for the music industry (mixers, DJ equipment, digital audio interfaces, microphones, etc.).

    More and more, powerful mobile devices are replacing laptops and portable computers

    And the need for USB audio doesn’t stop at professionals or ‘prosumer’ users, as it’s now readily accessible on many mobile OSs such as iOS and Android, and on hobbyist/maker SBCs such as the Raspberry Pi and BeagleBone Black.

    It’s a low-cost, low-power approach to the transport of digital audio and, at its best, can deliver a combination of high quality and low latency that the common wireless methods can’t match. But there’s the rub – you need to make sure it’s working at its best!

    The key problem that needs to be solved when replaying (or recording) high-quality audio through a USB interface is the generation of the necessary converter master clocks to a very high degree of stability and accuracy. Shortcomings in the audio clock recovery process caused by insufficient attention to detail at the design stage can easily result in measurable imperfections and clearly audible nuisance even to the average consumer.

    The audio industry has accumulated an immense body of work on determining the quality of reproduction and the audibility of impairments. It appears that this understanding of audio may have passed the current generation of microcontroller suppliers by, resulting in a generally rather poor standard of audio replay.

    That may be down to a tendency for pure-play MCU companies to treat audio as just another data interface format, without a real understanding of what’s important for achieving good audio quality. Most vendors acknowledge, from their app notes for example, that managing the time-domain integrity of reproduced audio data is critical to audio quality. But acknowledging the problem is one thing; solving it is another.

    Reply
  8. Tomi Engdahl says:

    Bridge chip simplifies audio data transfer
    http://www.edn.com/electronics-products/other/4458365/Bridge-chip-simplifies-audio-data-transfer

    Silicon Labs’ CP2615 bridge chip transfers digital audio data between USB and I2S (integrated inter-IC sound) serial bus interfaces without any code development. The part, which supports 48 kHz, 16 bit/24 bit stereo digital audio, can be used in a wide range of power-sensitive, space-constrained USB audio applications based on Android, Windows, Linux, and Mac operating systems, including headphones, speakers, MP3 accessories, navigation systems, and point-of-sale terminals.

    Samples and production quantities of the CP2615 digital audio bridge chip are available now. Prices start at $2.51 each in lots of 10,000 units. An evaluation kit is also available for $59.

    http://www.silabs.com/products/interface/usb-bridges/digital-audio-bridges

    Reply
  9. Tomi Engdahl says:

    Audio/Video Systems and Information Security
    https://www.theseus.fi/bitstream/handle/10024/108526/Korvakangas_Jari.pdf?sequence=1

    The purpose of this thesis was to investigate presentation technology systems
    and theirpotential security holes. Three different areas in audio/video
    were chosen for this. These were Video Conferencing, Audio over Ethernet and IP announcement systems. This study was carried out for Mission Critical Network team of Pöyry Finland Oy.

    Dante AVB/TSN, Ravenna and various other presentation
    technology systems are covered.
    Lastly, IP announcement systems are explained

    The analysis offered some solutions for Video Conferencing systems regarding how to avoid security breaches, but no obvious fix for all situations was found that would be easy to implement.

    Reply

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