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Very low volume spdif out, Is this normal?
Guineapig67
post May 30 2005, 23:24
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Hi all,
I have this digital sat receiver with optical spdif out, (it's an Opentel 3000ci btw), now I decided to buy a soundcard with coax spdif in

http://www.trust.com/14101

and built a simple adapter I found

http://www.epanorama.net/documents/audio/spdif.html

(the one which uses the 74HCT04)

Now coupling works perfectly and I can record from spdif but resulting files are very low in volume, even with receiver volume at maximum, typically peak at -12dB with the loudest radio stations, mp3gain usually applies 16,6dB gain on them, so I was wondering if this is normal or not...maybe it is?

Thanks for any suggestions.
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asral
post May 31 2005, 01:37
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QUOTE (Guineapig67 @ May 31 2005, 12:24 AM)
Hi all,
I have this digital sat receiver with optical spdif out, (it's an Opentel 3000ci btw), now I decided to buy a soundcard with coax spdif in

http://www.trust.com/14101

and built a simple adapter I found

http://www.epanorama.net/documents/audio/spdif.html

(the one which uses the 74HCT04)

Now coupling works perfectly and I can record from spdif but resulting files are very low in volume, even with receiver volume at maximum, typically peak at -12dB with the loudest radio stations, mp3gain usually applies 16,6dB gain on them, so I was wondering if this is normal or not...maybe it is?

Thanks for any suggestions.
*



It is usual for the satellite TV/Radio operators to keep the max level low (usually at
-10 db even if the programme material is highly compressed).

To check if your levels are attenuated by your card, connect a CD player via SP/DIF
and check the recorded level. If it is the same level with your rip of the same CD than your card isn't lowering the level.

If you are in Europe we might run a check on a commonly received station as I have
a similar system.
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Guineapig67
post May 31 2005, 06:39
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QUOTE
It is usual for the satellite TV/Radio operators to keep the max level low (usually at
-10 db even if the programme material is highly compressed).

To check if your levels are attenuated by your card, connect a CD player via SP/DIF
and check the recorded level. If it is the same level with your rip of the same CD than your card  isn't lowering the level.

If you are in Europe we might run a check on a commonly received station as I have
a similar system.
*


Hi asral and thanks.
I don't know if I have a cd player with an spdif out...I should check my pc cd players. Indeed I live in Europe, (Italy here), so a commonly received station maybe would be a simpler check. We could run a test recording of the same station at the same time if you like of course, I propose Swiss Classic tonight (Hotbird 12399GHz) at 17:02 GMT when it will air
Ludwig van Beethoven
Allegro con brio aus "Die Geschöpfe des Prometheus" Op.43

http://www.radioswissclassic.ch/

This radio station is one of my favourites and also happens to be one of the lowest volume.
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Guineapig67
post Jun 4 2005, 18:41
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Well, just to let anyone know, asral has some problems to do the test so we postponed it for the moment, in the meantime I found this radio test channel, it's

Hotbird 10775 GHz H 3/4

It states it's a +4dB 1 Khz test tone, I tried recording it with audacity and it turns out to be -36dB for me (with volume at maximum), could someone please try and confirm or not?

Thanks.

This post has been edited by Guineapig67: Jun 4 2005, 18:42
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asral
post Jun 4 2005, 22:23
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Still having a misaligned dish, let me clarify a point.

A +4 db level is relative to their system level. If their system 0 dB level is -40 db
than you may be recording a -36 dB signal stated as 0 db by the broadcaster.

Let me explain this better:
Fist of all most DAC's in satellite receivers can't handle full scale audio, so generally
the broadcasters set the maximum level broadcast to a lower level than full permissible
modulation to avoid distortion. This level generally lies at -5 to -15 db.

If for example the transmission you mention is for distributing to terrestirial FM transmitters
someone sets a 0 dB for their system and all FM exciters broadcasting that station is set
as that level for maximum FM deviation. If we take the above example their 0 db is set
to -40 dB maximum permissible digital modulation, so a +4db test signal would translate
to a -36 db PCM level. And dont forget they are using MP2, so they may decoding this
directly to analogue.

So don't translate these values to audacity's PCM levels. The MP2 decoders gain is important for the broadcasters.

But I have yet to receive this.

best regards
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precisionist
post Jun 7 2005, 15:49
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QUOTE (Guineapig67 @ May 31 2005, 06:39 AM)
I should check my pc cd players.

If you don't have any other audio SPDIF device to check your levels or to replace your converter (You could use an audio recorder with optical in and electrical out for that.), you can indeed check your computer drives. My Plextor claims to have a SPDIF out, but it's neither optical nor the usual chinch electrical plug...
Anyway, the analog volume of the signal in digital form shouldn't change. What is changed in the converter, is the "digital volume"- the voltage/current level of a 1 becomes a 0,8 (example) but is still recognized as a 1. Thus the audible volume shoudn't be changed.
QUOTE
This radio station is one of my favourites and also happens to be one of the lowest volume.
*

If it's a classical station, it should be quieter than the other ones. Be happy about that. smile.gif

Here I was talking with David about some British digital radio samples at lower volume than neccessary. It appears to be normal.


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