Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: SPDIF fundamentals - allowed audio data (Read 8341 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

SPDIF fundamentals - allowed audio data

I am trying to get SPDIF fundamentals right.

SPDIF only allows (constraints)
1) 2 Channel Stereo PCM
2) Frequencies of 32kHz, 44.1kHz and 48kHz.
3) Any compressed multichannel audio format equaling the bitrate of uncompressed stereo 16-bit PCM bitrate, which taking into account statement #2 gives 1024kbps, 1411.2kbps and 1536kbps.

Questions
1) Are there any constraints on bit depth of Stereo PCM?
2) Its impossible to send audio data higher in bitrate than Stereo PCM, but what about lower bitrates? Is that impossible too? Or does it have to be exactly equal to 16 bit Stereo PCM?

SPDIF fundamentals - allowed audio data

Reply #1 –
Quote from: ontherocks on
I am trying to get SPDIF fundamentals right.

SPDIF only allows (constraints)
1) 2 Channel Stereo PCM
2) Frequencies of 32kHz, 44.1kHz and 48kHz.
3) Any compressed multichannel audio format equaling the bitrate of uncompressed stereo 16-bit PCM bitrate, which taking into account statement #2 gives 1024kbps, 1411.2kbps and 1536kbps.

Questions
1) Are there any constraints on bit depth of Stereo PCM?
2) Its impossible to send audio data higher in bitrate than Stereo PCM, but what about lower bitrates? Is that impossible too? Or does it have to be exactly equal to 16 bit Stereo PCM?


SPDIF specifies two channel, up to 20 bits per sample, any rate (it is up to the sender and receiver to understand the rate).  Anything else is not strictly speaking SPDIF, but it is commonly adapted to handle 24 bit samples.
Teemu

SPDIF fundamentals - allowed audio data

Reply #2 –
So SPDIF can allow PCM bitrate 24bits and below at any sample rate?
I think there should be a upper limit to the sample rate, otherwise there won't be a upper limit to the bitrate.

http://www.cast-inc.com/cores/spdif/index.shtml however mentions the limits to be 3kHz to 192kHz
And this guy http://www.bigbrownbus.com/mixerton/whitep...dif/sp-dif.html says the upper limit to be 96kHz

SPDIF fundamentals - allowed audio data

Reply #3 –
There is a sample rate limit but much higher nowadays, maybe 768kHz.

The samples are sent as 32 bit words and there is space for 24 bits of audio data in each word, that limits the bits per sample.  You can send these samples at any rate up to the limit.

This article contains lots of technical details how it works, if you are interested.
Teemu

SPDIF fundamentals - allowed audio data

Reply #4 –
I was under the impression that it is impossible to send multichannel lossless compressed or uncompressed audio through SPDIF ONLY because of the upper limit in bitrate (which in turn is fixed by the upper limit in sample rate & bit depth).

But if there is no upper limit in sample rate (which means that there is no upper limit in bitrate) then why is that lossless multichannel audio cannot be sent through SPDIF?

SPDIF fundamentals - allowed audio data

Reply #5 –
Although it breaks the standard strictly speaking (or so I'm lead to believe), DTS and AC3 can be sent via S/PDIF perfectly happily by my $25 C-Media soundcard with the aid of d0gbert's modified driver.

Cheers, Slipstreem. 

SPDIF fundamentals - allowed audio data

Reply #6 –
Perhaps there was no point in adding new next-gen formats to the S/PDIF specification because no existing hardware could use them anyway. And last but not the least, S/PDIF is evil because anybody can re©ord and pi®ate the data travelling over it.

SPDIF fundamentals - allowed audio data

Reply #7 –
Quote from: Slipstreem on
Although it breaks the standard strictly speaking (or so I'm lead to believe), DTS and AC3 can be sent via S/PDIF perfectly happily by my $25 C-Media soundcard with the aid of d0gbert's modified driver.


DTS and AC3 are not lossless.

No, I don't know why you couldn't send lossless multichannel data over SPDIF as data like the other multichannel lossy codecs are sent.
Teemu

SPDIF fundamentals - allowed audio data

Reply #8 –
Quote from: Slipstreem on
Although it breaks the standard strictly speaking (or so I'm lead to believe), DTS and AC3 can be sent via S/PDIF perfectly happily by my $25 C-Media soundcard with the aid of d0gbert's modified driver.
No, that doesn't break the standard.
If age or weaknes doe prohibyte bloudletting you must use boxing

SPDIF fundamentals - allowed audio data

Reply #9 –
Oops! Apologies for the disinformation. I was under the impression that it was something "extra" as my soundcard wouldn't do it with the standard driver but did do it with the modified driver. It looks as though I have some reading to do. 

Cheers, Slipstreem.