Difference between revisions of "Audio Decoders"

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== TV Sound Standards ==
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{| border=1 cellspacing=0 cellpadding=5
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|TV-System 
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|  Sound Carrier  [MHz]
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| Sound Modulation 
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| Color System 
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| Country
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|-
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|B/G
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|5.5/5.7421875
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| FM-Stereo
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|PAL
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|Germany
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|-
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|B/G
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| 5.5/5.85
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|FM-Mono/NICAM
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|PAL
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|Scandinavia,Spain
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|-
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|L
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|6.5/5.85
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|AM-Mono/NICAM
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|SECAM-L
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|France
 +
|-
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|I
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|6.0/6.552
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|FM-Mono/NICAM
 +
|PAL
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|UK
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|-
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|D/K
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|6.5/6.2578125 D/K1
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6.5/6.7421875 D/K2
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 +
6.5/5.85 D/K/NICAM
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|FM-Stereo
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FM-Stereo
 +
 +
FM-Mono/NICAM
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|SECAM-East
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|USSR
 +
Peoples Rep. of China
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 +
Hungary
 +
|-
 +
|M
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M-Korea
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|4.5
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4.5/4.724212
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|FM-Mono
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FM-Stereo
 +
|NTSC
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|USA
 +
Korea
 +
|-
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|Satellite
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|6.5
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7.02/7.20
 +
|FM-Mono
 +
FM-Stereo
 +
|PAL
 +
|ASTRA
 +
|}
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==TV Sound Decoding ==
 
The TV sound needs to be decoded in order to receive an Audio Frequency (Sound_AF) signal.
 
The TV sound needs to be decoded in order to receive an Audio Frequency (Sound_AF) signal.
  
Historically this feature has been built into the tuner tin can, but this
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There are various possibilities
was only feasible for single TV sound standards. No programming was needed to get
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sound from the tuner.
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* Sound_AF provided by the tuner <br> Some tuners have mono out /stereo out /radio out
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* Sound_IF provided by the tuner, this needs an extra decoder
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** discrete decoding module (e.g. NE41S fpr BTSC stereo)
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** simple audio decoder chip (e.g. tda9820)
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** DSP audio decoder chip (e.g. MSP3415)
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*** all DSP audio chips provide Sound_AF
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*** some can provide I2S signal
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** Audio decoding function built into the PCI bridge chip (e.g. cx25840)
  
As an alternative tuners always had an extra output Sound_IF (Intermediate Frequency), which can be used by sound decoder chips to extract stereo or
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== Sound Routing ==
implement support for multiple sound standards.
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For stereo sound (and later Digital sound standards like NICAM) an
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There are multiple sound sources on the TV card, as there is only one
external chips (e.g. msp3415 or other) was introduced and needs to be properly supported by the linux driver.
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output, there must be a switch to select from these:
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* Sound_AF from tuner (mono/stereo/radio)
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* Sound_AF from decoder chip
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* Line In
  
For BTSC stereo also some discrete module (e.g. NE41S) exists on various cards.
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There can be these switches (aka mux or crossbars)
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* HEF4052: this selects from 4 inputs
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* some DSP audio decoder chips have multiple inputs
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* some PCI bridge chips have multiple input
  
The next step was the integration of the sound decoder into the PCI chip (e.g. cx25840 and others).
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If wired propoerly by the IHV, the I2S can be read directly by the PCI bdrige chip (so you have one less D/A -> D/A conversion, this should result in less noise).
  
Sound Routing
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== Sound Output ==
=============
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Another common problem are the multiple sound sources (e.g. Line In, Tuner Sound_AF, Sound-Decoder_AF) which have to be connected to the PCI interface chip.
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Sound can be output to:
As this chip only had one sound input, an external switch (crossbar) is required,
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* Line out
this is commonly a HEF4052 mux (but sound decoders can have also a crossbar).
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** Line out connected to sound card
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** Line out connected to active speakers
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* Speaker or headphone out (some cards had a headphone amplifier)
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* A/D digitizer on PCI chips (e.g. btaudio), this can be directly transferred to memory or can be sent to the audio card for output
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* also see I2S above
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[[Category:Technology]]

Latest revision as of 00:43, 3 May 2009

TV Sound Standards

TV-System Sound Carrier [MHz] Sound Modulation Color System Country
B/G 5.5/5.7421875 FM-Stereo PAL Germany
B/G 5.5/5.85 FM-Mono/NICAM PAL Scandinavia,Spain
L 6.5/5.85 AM-Mono/NICAM SECAM-L France
I 6.0/6.552 FM-Mono/NICAM PAL UK
D/K 6.5/6.2578125 D/K1

6.5/6.7421875 D/K2

6.5/5.85 D/K/NICAM

FM-Stereo

FM-Stereo

FM-Mono/NICAM

SECAM-East USSR

Peoples Rep. of China

Hungary

M

M-Korea

4.5

4.5/4.724212

FM-Mono

FM-Stereo

NTSC USA

Korea

Satellite 6.5

7.02/7.20

FM-Mono

FM-Stereo

PAL ASTRA

TV Sound Decoding

The TV sound needs to be decoded in order to receive an Audio Frequency (Sound_AF) signal.

There are various possibilities

  • Sound_AF provided by the tuner
    Some tuners have mono out /stereo out /radio out
  • Sound_IF provided by the tuner, this needs an extra decoder
    • discrete decoding module (e.g. NE41S fpr BTSC stereo)
    • simple audio decoder chip (e.g. tda9820)
    • DSP audio decoder chip (e.g. MSP3415)
      • all DSP audio chips provide Sound_AF
      • some can provide I2S signal
    • Audio decoding function built into the PCI bridge chip (e.g. cx25840)

Sound Routing

There are multiple sound sources on the TV card, as there is only one output, there must be a switch to select from these:

  • Sound_AF from tuner (mono/stereo/radio)
  • Sound_AF from decoder chip
  • Line In

There can be these switches (aka mux or crossbars)

  • HEF4052: this selects from 4 inputs
  • some DSP audio decoder chips have multiple inputs
  • some PCI bridge chips have multiple input

If wired propoerly by the IHV, the I2S can be read directly by the PCI bdrige chip (so you have one less D/A -> D/A conversion, this should result in less noise).

Sound Output

Sound can be output to:

  • Line out
    • Line out connected to sound card
    • Line out connected to active speakers
  • Speaker or headphone out (some cards had a headphone amplifier)
  • A/D digitizer on PCI chips (e.g. btaudio), this can be directly transferred to memory or can be sent to the audio card for output
  • also see I2S above