1 / 16

HDMI audio: capabilities, formats, testing

HDMI audio: capabilities, formats, testing. Thomas Kite Director of Engineering, Audio Precision Beaverton, OR. HDMI (high definition multimedia interface) is a standard for audio/video transmission between a source and sink over a single cable

adamma
Télécharger la présentation

HDMI audio: capabilities, formats, testing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HDMI audio: capabilities, formats, testing Thomas Kite Director of Engineering, Audio Precision Beaverton, OR

  2. HDMI (high definition multimedia interface) is a standard for audio/video transmission between a source and sink over a single cable • Provides for high definition video (up to 1920×1080p @ 60Hz, 48 bits per pixel) and high resolution audio (up to 192 kHz, 24 bits, 8 channels, uncompressed) • Standard on most new consumer A/V equipment: • TVs, DVD players, Blu-ray players, PCs • Camcorders, cellphones (soon) • Latest specification is Version 1.3a (HDMI Licensing LLC, November 10 2006) 2

  3. Three transition-minimized differential signalling data channels and a TMDS clock channel for video and audio Clock rate is (a multiple of) the video pixel clock rate Audio, metadata sent during video blanking intervals DDC (display data channel) for configuration Sink informs source of its A/V capabilities Optional CEC (consumer electronics control) bus for remote control information Signalling 3

  4. HDMI has huge bandwidth (up to 10 Gbps) on the TMDS lines Needed for high resolution video Video transmission method identical to DVI Audio and metadata are contained in ‘data islands’—packets inserted into the stream during blanking intervals At high video resolutions, plenty of bandwidth for high resolution uncompressed audio, lossily or losslessly compressed audio, or 1-bit audio (DSD) Audio capabilities reduced at low video resolutions (lower sample rates, channel counts) How audio fits in 4

  5. Audio support on HDMI • HDMI 1.0 (December 2002) • Linear audio: 8 channels, 192 kHz, 24 bit • Compressed audio: IEC 61937 up to 6.144 Mbps • HDMI 1.1 (May 2004) • Added support for DVD-Audio • HDMI 1.2 (August 2005) • Added support for 8-channel DSD audio • HDMI 1.3 (June 2006) • Added support for high bit rate lossless formats Dolby TrueHD and DTS-HD Master Audio 5

  6. Audio packets: N/CTS • The audio clock is not transmitted over HDMI • Rather, it is derived at the sink end from the video clock • Source computes integers N and CTS such that 128×fs = fTMDS_CLK×N/CTS • N is fixed for a given video and audio rate (table lookup) • Source counts TMDS clocks per audio clock to determine CTS • N, CTS transmitted in audio clock regeneration packet • The sink regenerates the audio sample clock from the received fTMDS_CLK, N, and CTS values • Asynchronous video and audio clocks, or audio clock jitter, cause CTS to change over time 6

  7. Audio packets: L-PCM/IEC 61937 • Formatted similarly to IEC 60958 • Allows for IEC 61937, which is built on IEC 60958 • 28-bit words: up to 24-bit audio, plus VUCP • 192-bit channel status block start also encoded • Supports up to 8 channels of linear 24-bit audio at192 kHz sample rate • Also supports IEC 61937 up to 6.144 Mbps (16-bit words at 192 kHz frame rate): • Dolby Digital (max 640 kbps) • Dolby Digital Plus (max 6.144 Mbps) • DTS Digital Surround (max 1536 kbps) • DTS-HD High Resolution Audio (max 6.0 Mbps) 7

  8. Audio packets: High bit rate • Added for HDMI 1.3 • Supports IEC 61937 above 6.144 Mbps • Used for lossless compression schemes: • Dolby TrueHD (max 18 Mbps) • DTS-HD Master Audio (max 24.5 Mbps) • Blu-ray discs have the capacity and bit rate to support these formats • Many current implementations decode in the player and transmit L-PCM over HDMI (works with HDMI 1.0) • Some receivers have decoders built-in, e.g. Onkyo SR-606 8

  9. Audio infoframe • Audio metadata sent at least once per two video frames • Some information is already in the audio stream: • IEC 60958 channel status bits (sample size, sample rate) • IEC 61937 burst info (coding format) • Audio infoframe adds extra information: • Speaker allocation for linear streams • Level shift value for downmixing • Downmix inhibit for DVD-Audio 9

  10. What about jitter? • Potential sources of jitter: • Jitter in the source audio clock • Jitter in the source video clock • Asynchronous audio and video clocks (causes CTS to change over time, usually over 2 or 3 values) • Poor performance of sink PLL • We found that the newest Silicon Image HDMI transmitter/receiver pair (9134/9135) is highly resistant to jitter • Injecting even high levels of jitter into the source audio clock produced no measurable jitter at the receiver 10

  11. E-EDID • Enhanced extended display identification data: a data structure supplied by the sink device • Informs source of the sink’s rendering capabilities: • Video resolution and interlacing • Video frame rates and color space • Number of audio channels and types of compressed formats • Enhancement of EDID, devised by VESA for computer displays • E-EDID is transmitted over the display data channel (DDC) • When source and sink are connected, source powers E-EDID ROM inside sink and reads it using I2C commands • Source is responsible for supplying data to sink in a form that the sink can handle: • Possible downconversion of video • Possible decoding, downsampling, and downmixing of audio • E-EDID is probably responsible for most HDMI problems 11

  12. CEC • Consumer electronics control: shares control information among all HDMI-connected devices • Offers convenience features: • One-touch play and record • Automatic source switching • Timer programming • System audio control • Single line connected to all devices in the chain • Automatic address discovery • Dozens of message types • Specification is almost as long as HDMI spec 12

  13. HDCP • High-bandwidth digital content protection: an authentication/ encryption scheme used by HDMI, DVI, and DisplayPort • All HDCP-compliant devices contain 40 56-bit keys • Source initiates authentication by sending 40-bit key selection vector (KSV) to sink • Sink responds with its own 40-bit KSV • If sink’s KSV is on the revocation list (stored on media), source will not proceed with authentication • Source and sink compute identical keys using counterpart’s KSV • Pixels encrypted/decrypted with these secret keys • Keys updated each video frame • HDCP probably the next most common reason for HDMI trouble: • HDCP repeater problems (try connecting devices directly) 13

  14. Testing audio over HDMI • Optional module for theAPx 585 audio analyzer • Generates linear, 8-channel, 24-bit audio • Generates compressed audio (Dolby Digital, DTS, MLP, DTS-HD MA) • Generates all standard video resolutions and frame rates • Auxiliary video input • Selectable HDCP encryption • Analyzes 8-channel linear audio • Audio/video monitoring 14

  15. Summary • HDMI has extensive audio capabilities: • 8 channels of linear audio at 192 kHz, 24 bit • Legacy lossily compressed multichannel formats • New lossily compressed multichannel formats • New losslessly compressed multichannel formats • HDMI has complex audio testing requirements: • Source devices must supply audio formatted correctly for sink, based on E-EDID • Possible transcoding in source • Many supported audio formats and sample rates • Sink devices must be able to handle all audio formats specified in E-EDID 15

  16. For more information • Please visit http://ap.com/products/apx_hdmi.htm 16

More Related