SAA7134 Audio Frequency

[Incast]

I was reading through this board and spotted this comment from Koepi a while back.

This issue is from the different timing between sondcard and tv-card. Some dshow capture applications allow you to select the sound input from the saa1734 (which is 32khz only from my experiences unfortunately).


This has left me highly confused. I've found plenty of Linux boards reporting that the SAA7134 only works properly in 32kHz.

However, I believe that these refer to TV captures only. This theory is strengthened by Philips Data Sheet which shows limited audio frequencies for TV audio but a wider range on more cards for other inputted audio not from broadcast TV. (http://www.semiconductors.philips.com/acrobat_download/datasheets/SAA7134HL_3.pdf pages 2/3)

Given that in VirtualVCR and Iuvcr I cannot find the sound input from the card as Koepi suggests could someone clarify to me what exactly the supported frequencies on the board are for TV and for capturing from other sources (eg. VHS).

[Wilbert]

This has left me highly confused. I've found plenty of Linux boards reporting that the SAA7134 only works properly in 32kHz.

However, I believe that these refer to TV captures only.
No, they probably refer to some TV card with a SAA7134 chip on it. I bet there are cards with a SAA7134 chip who do support 44.1/48 kHz. As you correctly say, the chip itself supports 44.1/48 kHz.

[Chainmax]

Is the Compro VideoMate Ultra limited to 32khz?

[Arachnotron]

The SAA7134 has it's own audio ADC next to the two video ones. You can access it directly using for instance a program like FlyTV which partly by-passes the driver. If you do that you can also cap sound from other sources then TV with it, provided your bord has a connector for it. (i.e. is a model with a loop-through cable). So it is not limited to TV only.

My Terratec has such a loop through; my Asus does not.

So you can choose if you want to use the internal ADC or an external sound card.

My guess is that there are stability issues with the internal ADC, since AFAIK it is not exposed through the normal drivers by any manufacturer.

FlyTV warns about stabbility issues too, and when I select the option I am limited to 16 bits, 32 kHz.

The chip however can do 48 KHz; The only reason I can think of for not having the option is that they fixed the driver on 32 kHz (= NICAM stereo sample rate) since nobody was ever goint to use it anyway.

Maybe some day I'll muck around a bit with writing directly to the registers involved. But my soundcard is 24/192 and will have better quality any day anyway.

[Arachnotron]

Having dug a bit more in the user manual:

It seems the ADC can do 48, but to be able to lock the audio sample clock to the video field frequency, both are locked to a 32 kHz reference clock to make sure that there is always the same predefined number of audio samples associated with a field. Which would be why the drivers are fixed to 32 kHz only.

[Chainmax]

Can I still capture with VDub if I use FlyTV? Also, do you have any idea wether the M-Audio Revolution has loop through? In any case, how does capturing TV's audio with the sound card work (i.é: is it captured separately and you have to mux later)?

[Arachnotron]

Can I still capture with VDub if I use FlyTV? Also, do you have any idea wether the M-Audio Revolution has loop through? In any case, how does capturing TV's audio with the sound card work (i.é: is it captured separately and you have to mux later)?FlyTV 2000 is a capture app, just like vdub. So you cannot use both at the same time, but installing flytv 2000 does not interfere with vdub.

The loop-through is not a feature of the soundcard but of the TV card. It simply means that there is a cable between the TV card and the soundcard line-in that transports the TV sound from the TV card to the sound card. So when capping TV, you select the souncard's line-in as the sound source in vdub or whatever. For convenience's sake, many TV cards offer a line-in connector, so you can still attach an external audio source without having to switch cables all the time. When you are not capping TV this is directly transferred to the soundcard again and the TV card remains passive. When you do cap TV, the TV sound is put on the loop cable and transferred to the soundcard.

Unless you have a SAA713x card, in which case you can choose to have either the TV sound or the line in on the TV card sampled by the SAA instead.

Whatever option you choose, the muxing will be done by the capture application.

[Inc]

Isn't the audiosignal of analogue TV broadcastings anyway limited to 15-16Khz ? Im not shure ....

[Incast]

Thank you for your excellent responses, especially Arachnotron (as always!).

My Terratec has such a loop through; my Asus does not.


My Asus has a loop through cable and I have always capped audio from the soundcard. Perhaps there are different revisions from that Asus model.

So if i'm reading what you're saying correct, the limitations arising from the ADC are not relevant if you are using the loop through to capture sound.

Am I correct in saying that the only advantage for using the ADC is to capture NICAM stereo recordings? (which are 32kHz anyway)

[Arachnotron]

My Asus has a loop through cable and I have always capped audio from the soundcard. Perhaps there are different revisions from that Asus model. :o :o Mine has too..... I forgot about it since it is part of a break-out connector I never use, since I use the Asus for capping TV exclusively. I have the Asus TV FM model B-TVFM-PAL-R3.0-ENG. It has a break-out connector with svid, composite and stereo sound in and an internal cable from the TV card to the soundcard.

[DrP]

Isn't the audiosignal of analogue TV broadcastings anyway limited to 15-16Khz ? Im not shure ....

Correct for most system's FM audio, so not a lot of point in sampling > 32k

[Arachnotron]

True for Tv sound and such, but HiFi VCR can go higher (VHS sound is actually better than casette tape). also, while TV sound is probably decoded 32 kHz internally anyway, in general you would like to have a little leeway above twice the maximum frequency.