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how to DIY MP3 with Dolby Digital and output in SPDIF?
how to DIY MP3 with Dolby Digital and output in SPDIF?
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Old 13th December 2007, 11:39 AM   #1
audio_novice is offline audio_novice  Taiwan
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Default how to DIY MP3 with Dolby Digital and output in SPDIF?

I am a project manager at a design company. I have a retail display project for a headphone company. Part of the requirement is a MP3-like solution to demo their Dolby Digital 5.1 headphones. I've considered MP3 and DVD players. Problem with MP3 is that it is not SPDIF and Dolby Digital. Problem with DVD (with SD or USB slot) is the wiring. They have specific wiring requirements to ensure that it can connect to their headphones.

They gave us the following specs:
1. Digital audio output (SPDIF) to connect with 2 types of headphones:
A Type: 4 wires
- 2 for +5v +GND
- 2 for SPDIF
Power consumption < 130 mA@max
B Type: 5 wires
- 2 for +5v +GND
- 3 for R, L, Audio Ground
Power consumption < 110 mA@max

Power is needed to power the headphones.

2. Flash Memory via SD card or USB (1 gig to contain 30 sec loop)

3. Control: "play" button must be pushed for music to play. music stops after it is played. music starts again only when "push play" button is pushed again.


I am not an engineer and so dont understand what they mean by their 4 - 5 wires requirements, or how that can be connected to the Digital Audio output on the back of DVD players (coaxial or Toslink). Any help would be appreciated.
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Old 13th December 2007, 01:49 PM   #2
Pulse-R is offline Pulse-R  Australia
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this is the way I understand it:
the 2 wires (of the 4 wire output) for S/PDIF would be the same as the coaxial digital audio (S/PDIF) output from the DVD player.

the 3 wires L,R, GND (of the 5-wire type) would be analog stereo mix-down from the DVD.

as the headphones are active, most likely line-level signals.
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Old 14th December 2007, 04:16 AM   #3
audio_novice is offline audio_novice  Taiwan
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thanks.

For Audio signals
"4 wire combination"
the 2 wires for SPDIF / is there a coaxial to "2-wires" connection? my question is how
can this be connected?
"5 wire combination"
the 3 wires (L,R,GND) / can that be done via just standard RCA jack (L,R - red & white)? but how about the GND?

to power the headphones (2 wires for +5v +GND; Power consumption < 130 mA@max or <110mA max) - do you have any recommended solution

Thanks.
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Old 14th December 2007, 05:34 AM   #4
purplepeople is offline purplepeople  Canada
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Regarding 4-wire connection: Maybe the headphones have an built-in DAC for direct input of digital signals.

Assuming that is true, then the only predictable user would be studio engineer or other audio professional.

I'm curious... is your company one of the large pro audio supplier? Mackie? Digidesign? M-Audio?

ensen
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Old 14th December 2007, 12:29 PM   #5
audio_novice is offline audio_novice  Taiwan
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I am assuming that it has a DAC built in (because of request for SPDIF).

But again the 5 wire combination leads me to think that the feed need to be analog.

No, it's actually for the average consumer. sorry I cant divulge too much as it is a pending project.

No. I work for a production company in Taiwan. We specialize in building customized retail display stand. We are working with a company in the States that owns the account. So basically they would outsource the work to us and leave us to figure out all the details to get to their customer's vision.
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Old 14th December 2007, 10:01 PM   #6
purplepeople is offline purplepeople  Canada
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Ah... consumer user.

The analog input would be standard for hook up to most MP3 players. The digital input would be for hook up to other devices... maybe PC sound card or DVD player digital output.

If the internal amplifiers have good SNR, that would explain one need
for digital input. Common sound cards and cheap disk player have horrible analog outputs but reasonable digital output.

For POP display, maybe the client requires hidden player using the digital input and external plug for connecting customer MP3 player. When the customer want to try the headphones, they can use POP display player or connect their own iPod or cellphone, which is already loaded with familiar music.

:)ensen
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Old 14th December 2007, 10:10 PM   #7
Pulse-R is offline Pulse-R  Australia
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s/pdif gnd is the rca outer, and s/pdif signal (+) is the inner of the rca.

yes, using the red/white for left/right. again, the gnd is the outer of the RCA plug.
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Old 14th December 2007, 10:13 PM   #8
purplepeople is offline purplepeople  Canada
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Wait... I always thought that red was always right and white or black was left.

:)ensen
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Old 14th December 2007, 10:17 PM   #9
Pulse-R is offline Pulse-R  Australia
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oh, I guess I shouldn't assume that everyone knows

yes, left = whiteor black, red=right

a little OT, but what about front/rear surround and centre... do they have standard designations?
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