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Old 27th August 2004, 09:33 PM   #21
lucpes is offline lucpes  Europe
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If the sine waves are full-scale (0dB digital) it's normal to get clipping/distortion.

Try burning tones say with the amplitude in these limits: -3dB @ 20Hz to -18dB @ 20kHz.
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Old 28th August 2004, 12:02 PM   #22
Vortex is offline Vortex  Hungary
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Quote:
Originally posted by jneutron


Using a sine wave generator, record in your computer a wave file which goes from 20 to 20Khz. Keep it about 80 % of full scale.

Make a CD of that.

When you play back that CD, you will initially hear just the sine wave.

As the frequency goes up, on a poor player, you will begin to hear subharmonics..My computer sound blaster card starts to do this at about 4 Khz..it sounds like heterodyne whistling (ask some other old fart what that is...I'm gonna be in vacation mode in about 10 minutes..)

The depth of the reconstruction filter will determine the extent and amplitude of these subharmonics..since the reconstruction filter is not infinite in length, the subharmonics will be there. However, it is not very difficult to exceed the output quality of my sound blaster...

Cheers, John

You are absolutely right.

Another matter may be that Sound Blaster Cards may not pass digital signal out on their digi-out very good... I'm using a digital receiver, connected via coaxial cable to the Sound Blaster, another coax-in connectec to the CD Player (which is connected analog, too).

I made a quite long sweep of sine wave from 20Hz to 20KHz with Steinberg WaveLab's signal generator, then I burned it onto Philips CD-R 80 with 4x.

Well, the result is surprising. Playing the wave from the PC via the SB results in some strange odd low-level noises at higher frequencies, some kind of whistling or I don't know but something's there. Quite annoying, needless to say. As if a station-searching old military radio would sound near the sine wave (at a much lower level of course, but good audible).

The same if I put the completed CD onto the CD player, everything set to digital playback - still the same.

If I play the burned CD on the normal CDP, this noise simply isn't there. Just the pure sine wave. That was via coaxial connection, so the amplifier's DAC did the job. In analog connection, the CDP's DAC chips did the same job - no annoying noise.

Although I altered the CDP.. two DAC-s inside, namely BB PCM56-s. I cut two legs of the chip off the PCB board, soldered them together and finally soldered these two legs to the analog RCA out warm point with a 100-Ohm resistor in series (RCA warm point cut off from the PCB of course, too). The result was astonishing for me, the CDP got it's shining in the high's. I think I bypassed the filter circuitry completely after the DAC chips with this method, and just as said before, it shouldn't be better always.. I don't know, I like it much more, it's so light, airy ... dunno. (Probably subjective since we have different ears and sensitivities..) But anyway, still no additional noises I can hear near the sine wave, so I think Sound Blasters have all the same crappy digi out interface where something went really wrong at the design/or manufacturing... or internal PC noise, bad "shielding" (no at all).. I don't know ...

On the other hand, for that money... SB Live 5.1 digital costs about $10-20 or even less... don't await much from it.



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Old 28th August 2004, 12:30 PM   #23
lucpes is offline lucpes  Europe
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Quote:
Originally posted by Vortex

Another matter may be that Sound Blaster Cards may not pass digital signal out on their digi-out very good... I'm using a digital receiver, connected via coaxial cable to the Sound Blaster, another coax-in connectec to the CD Player (which is connected analog, too).

I made a quite long sweep of sine wave from 20Hz to 20KHz with Steinberg WaveLab's signal generator, then I burned it onto Philips CD-R 80 with 4x.

Well, the result is surprising. Playing the wave from the PC via the SB results in some strange odd low-level noises at higher frequencies, some kind of whistling or I don't know but something's there. Quite annoying, needless to say. As if a station-searching old military radio would sound near the sine wave (at a much lower level of course, but good audible).

The SB Live! internally resamples everything (44.1 in your case) to 48kHz and it's known for it's bad quality whilst doing it so this is what you hear from the PC playing a wave sweep.
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Old 28th August 2004, 12:33 PM   #24
MikeB is offline MikeB  Germany
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Hi !

Some note on soundcards from a games programmer....

AAARRGH !

Most of the soundcards are really crap, some explanation on digitalout:

You have a wave with 44.1khz, right ? Okay, you set the digout to 44.1khz, right ?
Now you might believe that the sounddata goes unmodified to the digout...
Way wrong !
The soundcard mixes internally everything with 48khz. So your 44.1khz
signal is upsampled to 48khz, mixed + volumecontrol, then downsampled to 44.1khz...

Unless the waveplaying-software has direct access to the SPDIF, you
can forget soundcards...

The only way to get proper signal is to set digout to 48khz, and play
samples with 48khz.

This applys to nearly all soundcards...

Better soundcards/drivers would switch mixing to the samplerate
the digout uses.

Have you ever been able to play a DTS-encoded CD with the PC ?
Me not...

Older soundblastercards did this up/downsampling without filtering !
So pitching samples sounded somehow funny...
Now i pitch samples with my own routines, using CPU.

Mike
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Old 28th August 2004, 12:47 PM   #25
Vortex is offline Vortex  Hungary
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DTS signal is 96KHz as far as I know, that's may be the problem.

Tell me if I'm wrong.
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Old 28th August 2004, 12:58 PM   #26
MikeB is offline MikeB  Germany
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I think you are somehow wrong.
At least the signalcarrying is plain 44.1khz, that's why you can play
a DTS-CD in any CD-player with digitalout.

I am not sure if the DTS-decoder uses another samplerate.
AFAIK it doesnt...

For Dolbydigital the samplerate supplied by the stream is the
samplerate for playback.

For this reason you can burn dobydigital with 44.1khz on a CD
and play it with a normal cdplayer. The decoder correctly plays this.
Of course you need a software that correctly formats the DD-frames
to the 2352 bytes of one audiocd-sector. (with paddingbytes)

Mike
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