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Old 12th July 2002, 03:46 AM   #1
jleaman is offline jleaman  Belgium
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Default Digitial AUDIO

I have a question i have been looking for a simple answer to my question .. ok here it goes

On the back of my dvd player/mp3 player it has left right and coax out ( digitial out ) now when you guys talk about dac's is that to make the digitial out on m dvd work on a normal amp like one with rca's left and right ?? if so are they hard to build ect ect and where can i research and mabey build one that is designed and works so that i can play with im interested in using my dvd because it is a nice unit and i payed a fair bit of coin for it.. can you help please any one.. thanks

just a question that is all..

NO one disses people who answer questions..

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Old 12th July 2002, 05:00 AM   #2
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DAC = Digital to Analog Converter.... It converts a digital signal (bit stream signal, discrete time) into an analog signal (continuous signal).

I think for DVD, converting digital signal to analog is not as simple as we think. Correct me if I'm wrong, but I think the DVD player only provide ONE digital output jack. So, you have to know the format of the data. To complicated matter, the digital output signal of DVD is in the form of light.

I think the format of the digital data is for 5.1 surround.... So, one frame of data contains 6 channel information. I once try to find the format of this data in 5.1 surround (THX and the like), but I came out empty handed.

Probably, we have to use 5.1 decoder chip. Has anybody try to make a DIY 5.1 surround decoder?

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Old 12th July 2002, 07:43 AM   #3
hifiZen is offline hifiZen  Canada
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JasonL:

That's right. An external DAC is for converting the digital data into a voltage waveform that can be amplified and played back through your headphones/speakers. There are of course DACs built in to your player, which output to the left and right RCA connectors, but you can often build better sounding DACs. The digital output is there for just such a purpose, and external DACs can be relatively simple and rewarding projects.

Here's everything you always wanted to know about DVD audio formats (if you just want your question answered, you can skip to the end bits):

To start with, there are a number of things you should know about the digital output on a DVD player vs. the digital output on a CD-only player. In the world of CDDA (standard CD music, often refered to as Compact Disc Digital Audio or CDDA), there is only one data format: 16bit, 44.1kHz PCM, 2 channels. Every CD player can read this so-called "redbook" format and play it back, as well as send that data to the digital output as 16/44 PCM. So, it is easy to build an external DAC, as there is only one format of data to handle.

By contrast, the DVD standard was designed to be extensible, which means that there are now a large number of data formats for storing audio on the disc... MPEG2, AAC, Dolby Digital (DD), DTS, raw PCM, MLP, etc. To make matters worse, many of these formats are capable of supporting different bitrates / sample rates and different numbers of channels (2, 3, 5.1, 7.1 etc...). Often times, there are even multiple formats present on the disc at the same time. For example, DVD movies almost always have a DD soundtrack in both 2-channel and perhaps 5.1 channel surround as well. The same disc might also have DD tracks in other languages, along with a higher-fidelity DTS soundtrack which can be played back on systems equipped with a DTS decoder. Confused? Welcome to DVD... Unfortunately, that's the nature of the beast, but it's not really all that complex when we get right down the practical aspects of playing DVDs, as I'll explain later...

Almost all DVD players support the basic formats which have been around since the advent of DVD - PCM, Dolby Digital and MPEG2 audio, as well as CDDA. MPEG2 and PCM are rarely used in region-1 movies, so in general, DD is what you're dealing with for movies. When playing a regular CD, the digital output should be 16/44 PCM.

If you have a newer DVD player, or perhaps some of the high-end previous generation players, you may have DTS support. Now DTS and the player manufacturers did something sneaky: they put DTS logos on all players capable of reading the DTS data off the disc. BUT, this does <i>not</i> necessarily mean that the player can actually decode the DTS format and play it back for you!!! One must look very closely at the DTS logo to see if the fine-print at the bottom of the logo says "Digital Out" or "Digital Surround". If it says "Digital Out" it's what I like to call a "dumb" player. It just reads the data off the disc, and spits it out to the digital output without doing anything further. That's all fine and dandy if you have an external DTS decoder, but if not, then this DTS data is useless to you. If, however, the player has a DTS "Digital Surround" logo, then the player will actually go to the trouble of decoding the DTS data format into something useful for you, like PCM.

The last major audio format for DVD is Meridian Lossless Packing, or MLP. This is used for really high-quality audiophile DVD music, and usually exists on DVD-audio discs marked with the MLP logo or the "Advanced Resolution" logo. This is super-high quality audio encoded on the disc in a losslessly compressed format. Players capable of decoding the MLP format extract this data to either 24/96 PCM or 24/192 PCM, which is some 1100 times more resolution than CDDA!

Now for the practical stuff: what comes out of the player's digital output when I'm playing X format, and how do I build a DAC to handle that digital output? The answer: it depends on the player... most players will have a setup menu from which you can select the digital audio output format. For compatability with a home-built DAC, what you want is PCM (aka LPCM). Other formats ("bitstream, "DTS", etc.) are not easy to handle with a home-built DAC, or cannot be used without a proprietary decoder (nearly impossible for a hobbyist to get). If you select PCM, then most or all formats that the DVD player can read and/or decode should get converted to PCM format before being output on the digital output jack. Once again, there is one small caveat: not all players will output full resolution PCM data on the digital output, and it is generally restricted to two channels only. Most players will restrict digital PCM output to 24/48 data by downconverting higher resolution 24/96 or 24/192 data. There are, however, a few models which will output 24/96 PCM data, though I haven't seen any with digital PCM output of 24/192.

Anyway, that's the main stuff you need to know. As far as building a DAC, there are plenty of DIY designs out there... just do a search on www.google.com for "DIY DAC" and I'm sure you'll come up with dozens of projects, some more advanced than others. You can also search this forum for ideas and good designs. For maximum versatility, you'll want one which can handle everything from 16/44 to 24/96 PCM input. For reference, the standard interface used on CD and DVD player digital outputs is called SPDIF or IEC958, so this will be the format that the outboard DAC receives.

My personal recommendation for a starter DAC would be something with the following chips: CS8414 and either the CS4396 or CS43122. Just those two chips plus a good pair of opamps such as the AD8610 (and of course the various support circuitry) will produce a fantastic stereo DAC.

For your first project, you should probably avoid more advanced DAC features like: ASRCs, FIFO buffers and PLLs, separate digital filters like the DF1704 or SM5842, PMD-100 etc. Stick with a simple 2-chip design and you should be able to successfully build a DAC 98% as good as the more advanced designs.

Have fun!
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Old 12th July 2002, 07:44 AM   #4
hifiZen is offline hifiZen  Canada
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hmm... maybe I should write a book.

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Old 12th July 2002, 08:15 AM   #5
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Thumbs up BRAVO!!

How bout the analog Audio DVD output (RCA) ? If it also produced by built in DAC of DVD from PCM format, then it will be no point making external DAC just to convert the PCM digital output, right?


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Old 13th July 2002, 11:12 AM   #6
hifiZen is offline hifiZen  Canada
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Pretty much... Inside a DVD player, everything gets converted to a PCM format for the internal DACs. But, chances are you can do better by building your own external DACs. Of course, another good option is to modify the player's internal DACs and analogue output stage - then you don't have to worry about digital interconnect and the associated data handling chips. You also don't have any of the PCM format restrictions which may accompany the player's stock digital output.

The only real exception to the use of PCM format by DAC chips is with Sony's SACD format known as DSD (and even then, not in all cases - some players convert DSD data to PCM for the DACs)... but SACD is a different beast entirely, and sufficient material for another thread altogether.
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