24 dB quiet on ADAT output

[bitcrusher]

Hi Muse!

I have my Receptor to a Creamware PulsarII card on my PC via optical (ADAT) connection.

The output from Receptor is 24 dB too quiet, I assume this is a 20-bit versus 24-bit issue.

Anything I can do on the receptor side? I can add the gain after of course, but its enough of a nuisance just to simply forego optical which makes me sad.

I don't have this problem between my mac and PC via the same optical (digidesign ADAT bridge and PulsarII).

Best,
Steve

[Bryan@MuseResearch]

Hey there

We've run a variety of tests today, and it appears that our ADAT output on Receptor is correct, so we think there might be something wrong on the Pulsar side.

We tested the levels using a sine generated by mdaTestTone (included on Receptor, hopefully you didn't trash it, its a fairly handy program) adjusted it to a 1kHz, OdB Sine wave. Using default mixer settings and assigning it to any of the ADAT outputs, we see 0dB on the ADAT XT we have in the office, and then repeated the test using an E-MU 1820 interface connected to a Windows PC, and we see the same level - 0dB everywhere you look.

it would be helpful if you would repeat the same test with your setup.

Are you sure that Pulsar is set to to the proper bititude (forgive the expression)?. I will also check it with Nuendo using an RME interface, but I suspect we will see the same thing...

If you can provide more details about your setup, perhaps we can provide a little better guidance... feel free to send me a mail directly if you would like.

All the best

Bryan Lanser
VP Business Development and MaxReverb's stand-in while he's on vacation!

[bitcrusher]

Hi Bryan,

Thank-you very kindly for your detailed reply.

I'd be happy to blame the Pulsar!

Here's the peculiar part - the test you mention works fine on ADAT 3-4, ADAT 5-6, and ADAT 7-8.

The Master fader in Receptor is at unity, and the meters in receptor in are drawing to the top. However the 1-2 output is exactly 4 bits less (24 dB) on the ADAT output. My Receptor hardware is 1.0 rev B.

I've never noticed such a problem before, so I do suspect there is something *potentially* odd with the bit-depth on the ADAT 1-2 out from Receptor.

So, this is not a "practical" problem now that I noticed I have 6 outputs on the light-pipe working fine, so this is enough for my needs.

Nonetheless, I'll hook up the Receptor to my ADAT bridge today and do the same test, this should help find the culprit.

I'm really *loving* Receptor - it's a killer box!! It runs all my custom-built VST's like Lucifer and Minion without a hitch. I even have GURU with multiple outputs working like a champ!

Now that I'm learning guitar, it has even more use to me than ever before Thanks again for the reply.

best,
Steve

[bitcrusher]

I've discoved the problem, not sure if it is "pilot error" or a software bug in Receptor:

In the Output Assignment window, if I use the Master Bus, I lose the 24 dB. I was using it this way, because you can't disable the ADAT 1-2 from the master bus.

Here's a screenshot showing both conditions (the receptor output assignment showing is all that I've changed in the two sections).




-Steve

[bitcrusher]

eek, the front-panel volume knob also controls the ADAT output. I had no idea! I figured it was an analog-out attenuator.... but this makes sense...

Pilot Error, problem solved!!

[Bryan@MuseResearch]

Glad to hear you've got the situation under control, but I think I'd better point out an important architectural thing that may be contributing to the situation:

Its important to remember that when a channel is assigned to the master bus, it will pick up some additional gain, which makes it hotter than a direct assignment to ADAT 3/4, 5/6, or 7/8. This is because we have a default condition in hardware that assigns the master stereo bus to ADAT 1/2, so if the Receptor channel you are using is assigned to BOTH the ADAT 1/2 bus as well as the master bus, then it will be 6dB hotter than a direct assignment that does not go through the master bus. Bringing down the front panel audio brings down the mix bus level in hardware, which stops it from appearing so hot.

Why the Pulsar is behaving strangely is beyond me. Creamware makes some excellent products, so I'd be surprised if wrapping is a problem, but I know that a lot of digital systems will "wrap" in a digital overload condition, like in the case where you supply a 24 bit signal to a 16 bit input ending up appearing like an 8 bit signal. Perhaps the Pulsar is set to allow only 16bit inputs?

Anyway, sounds like you have a handle on it, and by the way, I double checked with the RME interface on a mac, and the ADAT outputs on Receptor behave exactly as you would expect...but the ADAT 1 and 2 signal is hotter than the others _until_ you remove it from the master bus assignment, then they are all equivalent.

Just be sure to remove a Receptor channel from the assignment to the master bus if you want all the ADAT output levels to match!

One more thing - one of my favorite tricks with Receptor is to assign the effects busses to ADAT outputs and remove them from the stereo master bus. This essentially turns Receptor into THREE separate stereo mixers, and when used with an ADAT to audio converter such as the Behringer ADA8000 (don;t let the price fool you, its actually an amazing little box!) then Receptor suddenly becomes a very versatile system for surround, or post work where you want different stems with different effects assignments on them, or even for sending unaffected signals to monitor mixes and effected signals to FOH systems for live use. Cool, huh?

Cheers

Bryan

[bitcrusher]

Hi Bryan,

thanks again for the help.

It was just the front-panel volume knob of the receptor - I had no idea this was a digital control.

Just my (bad) luck, I had it set to a level that provided *exactly* 24.0 dB of attenuation... so I jumped to a "4-bits" conclusion... whereas any other setting on that knob would have probably made me think otherwise.

Thanks for the tips and the sunday-support! I'll keep things off the master bus when level-matching is crucial!

back to learning guitar scales....!

Best
Steve

[DanTimis]

You figured it out: the front panel VOLUME knob is a digital attenuator that is applied after the master fader. Unfortunately, there are no separate meters for it. You can use the master fader to attenuate or boost the volume. The front panel knob is only an attenuator. At it's maximum position it is 0dB.

The reason the VOLUME knob is affecting the ouputs and not just the headphones is that if you are performing live and suddenly things are very, very loud, you can turn the front panel knob down very easily. The analog outputs and the ADAT 1-2 are tied together so whatever affects the analog outs it also affects the ADAT 1-2.

If you assign the ADAT 3-8 to the master fader they will also be affected by the front panel VOLUME. You do have the option of assigning them to individual channels or to a bus like Bryan explained, in which case they will not be affected by the front panel VOLUME.

The only output coming from the master that bypasses the front panel VOLUME attenuation is the S/PDIF output. This allows you to record the main stereo outs, or to send them as your main outputs and at the same time use the analog outputs or headphones for monitoring. With the VOLUME knob you can set a separate monitoring level this way.