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Digital monitoring control with 82xx/72xx series

baguette, modified 12 Years ago.

Digital monitoring control with 82xx/72xx series

Youngling Posts: 7 Join Date: 6/24/09 Recent Posts
Hi there,

I am in the process of switching from 8050s to a fully digital/dsp setup in my studio. I currently have a pair of 8240s, a 7260 subwoofer and the GLM AutoCal package on loan for testing. My experience so far is that the new system is absolutely brilliant in terms of accuracy and control and represents a valuable improvement over my previous, analogue system. This is even more impressive as the 8050 is a brilliant monitor in itself!

However, I have some questions regarding routing and controlling different soundsources and signals with the 8240/7260 system.

I am currently using the Griffin PowerMate for controlling volume, muting and bass management. This works pretty well as long as the routing scenario stays simple. What I haven't figured out is how to introduce master section -level monitor and sound source control functionality into this setup.

I need to be able to switch between sound sources and output destinations (Active Avantones) on the fly, as well as sum to mono and dim from a monitor controller -type device - as I have been doing with my analogue setup until now.

To add to the challenge, I am using Pro Tools HD and the AES -signal to the speakers comes directly from my PTHD i/o (Lynx Aurora 16). This is all fine and well when using only Pro Tools. But I also need to check other Core Audio based sources like iTunes for musical reference etc. - while I'm using Pro Tools. Of course, the Digidesign Core Audio driver can't be used when Pro Tools is running, which only leaves me the option to use Pro Tool's auditioning feature in the Import box. With a 60+ Gb iTunes library this workflow is clumsy to the degree of not being useable at all and I need to find an elegant and permanent solution to this issue.

Having explained the background I can finally get to the actual questions:

1) GLM vs. separate digital volume controller/master section:
As it happens, TC Electronic just released a monitor section controller called BMC-2. This product seems to be the first of its kind (outside the broadcasting world) and does offer most of the functionality I need: monitor and source switching, level control, dim, mute and mono for both AES-AES as well as analogue-analogue.

But will this method of attenuating the digital signal create an inferior signal quality to the 8240/7260 compared with using the GLM software for volume control? I use 24 bit exclusively in ProTools but 16 bit or less in iTunes.

And if the quality is significantly worse, can this be remedied by proper calibration?

I am not asking you to judge the quality of the BMC-2 itself but rather if the 82xx/72xx/GLMs proprietary, built-in principle and implementation for digital volume control create a significant advantage over the principle employed in the BMC-2 and, I assume, in most full-blown digital mixer boards?

http://www.tcelectronic.com/bmc-2.asp

2) Optimal gain structuring for GLM with separate digital volume controller/master section:
What is the optimal digital gain structure if I decide to use a separate digital monitor controller? What level should I "lock" the GLM permanently to in order to optimize the gain structure and sound quality? Is it really 0dB or would that unnecessarily tax the analogue amps in the speakers in some way? How does a 82xx/72xx system actually behave in this regard, when used in stored setting/stand-alone mode - is the DA stage always at max 0dB level in this case?

3) The analogue route w double conversion
I could stick to an analogue controller, of course, and work around most of these issues that way. However, I would then introduce an additional AD and DA roundtrip. It would also necessitate buying an expensive separate high-quality AD/DA stereo converter box or, alternatively, a monitor controller unit with pristine integrated AD/DA.

How do you view this alternative from a technical point of view? Would going the analogue route result in a better or worse quality signal compared to using a separate digital controller as described above. - assuming that the analogue/ADDA path is of a decent quality (like Dangerous Music, Crane Song, Lavry Black etc.).

4) Or, should I not worry about these things at all? ;)

I thank you in advance for helping me figure this out. Sorry for the long post...


Regards,

Christian
ilkka-rissanen, modified 12 Years ago.

Re: Digital monitoring control with 82xx/72xx series

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
If I understand your problem properly, you want to use an AES/EBU source and an analogue source with your monitoring system. Unfortunately TC Electronic BMC-2 does not seem to have an analogue input, just three digital audio inputs. It seems to have a DA-converter function and you have the option of using digital audio or analog audio as the method for linking down to your monitor loudspeakers.

(a) Monitoring in mono using GLM

GLM software can use System Setup files. Each System Setup file defines the monitor system cabling and acoustical calibration. You can use System Setup files to force selection certain input signals. This means you can create a system setup file for a stereo pair of speakers where both speakers are listening to the A and B channels in the AES/EBU audio. This puts your stereo pair into a Mono mode. Normally, your left speaker is reproducing one of the channels, say A, and your right speaker is reproducing the other, say B, and you get stereo reproduction. The subwoofer is listening to several audio channels all the time, so no changes are usually needed there. So, to switch from stereo to mono reproduction using GLM, you create to System Setup files, one for mono and one for stereo. This can be easily done by taking a copy of your existing System Setup file, and editing in the copy the channel settings manually to turn on reproduction for both A and B channels for both loudspeakers. This method can be used for AES/EBU signals.

(b) Optimizing the processing chain for analog source monitoring in the stand-alone mode (without computer and GLM).

To optimize the signal processing chain for signal quality in stand-alone mode and using analog signals, it is usually a good idea to drive the possible AD converter using an analog signal as high as possible to keep you safe headroom for clipping. When the Genelec DSP loudspeakers are operated in the stand-alone mode (without GLM) the volume setting defaults to 0 dB FS (full open) after a loudspeaker re-start. This usually results in signal level that is too high. Then, you want to bring the speaker back on the GLM control network, and go into each loudspeaker's settings in GLM, and edit down the Level setting in the Acoustical Editor. Usually good analog system calibration is found when the input sensitivity is decreased by about 10 dB from the value set by GLM AutoCal. Do this for all loudspeakers and subwoofer(s). For each loudspeaker and subwoofer, save the settings in the loudspeaker/subwoofer for stand-alone operation. Now remove GLM and restart the loudspeaker system. Now you are in stand-alone mode (working without computer and GLM) and you are able to use conventional analog signal level control to adjust the monitoring level.

(c) Switching between separate AES/EBU sources

GLM can provide volume, dim, mute, and mono, but not source switching. Unfortunately Genelec loudspeakers do not provide multiple parallel AES/EBU input or the possibility to switch between them. However there are signal cross switch routers available on the market that can also be used for AES/EBU, and these can provide the ability to select between several AES/EBU signals. When you are using analog signals and you have a DSP subwoofer in the system, you need an AD converter (for example Genelec AD9200) before the subwoofer.

(d) Volume control in 8200/7200 vs. at the source

The volume can be controlled at the signal source (Protools, BMC-2, or some other source). It is always advantageous to have the volume control as the final action before the signal hits the drivers in a loudspeaker. This is why it is a good idea to use the volume control provided in the Genelec DSP loudspeakers and GLM. This is particularly useful if your source audio is using 16 bit word length. One good reason for this is that you may not know exactly how well your source is implementing the level control function. I have to point out that for most professional audio processing gear, the implementations are good, and no major problems should be expected. However, it is still a good idea to save the level control as the last action before the audio hits the drivers.

(e) Several AD-DA conversions

AD and DA conversions are always noisier than pure digital audio signal processing. Several cascaded AD-DA conversion stages should always be avoided if possible. AD and DA technology simply is not as quiet as DSP even if significant progress has been made over the last several years.

Your questions are relevant and important. You are doing the right thing optimizing the performance of your signal monitoring chain for the best performance.

GENELEC
Aki Mäkivirta
R&D Manager, DSP Products
dmac, modified 5 Years ago.

Re: Digital monitoring control with 82xx/72xx series

Youngling Posts: 5 Join Date: 8/18/13 Recent Posts
Just purchased (2) a8260s and (1) 7270a. I would like to send an unconverted, digital signal to the 7270 and allow the Genelec DA to perform conversion. Do you know of any multiple digital inputs to stereo AES output to the 7270 available? Its seems you are suggesting that using the GLM systems to control volume, perhaps with the new remote genelec volume controller is the best?
ilkka-rissanen, modified 5 Years ago.

Re: Digital monitoring control with 82xx/72xx series

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
Hi,

What is your source device? I recommend using GLM for the volume control, either via the software or wireless/wired remote controller.
dmac, modified 5 Years ago.

Re: Digital monitoring control with 82xx/72xx series

Youngling Posts: 5 Join Date: 8/18/13 Recent Posts
The sources will range from Apple TV (opt), CD (COAX or Opt)...rarely direct from computer. I am not in the business of studio recording, i have many friends in the space though and just got to liking their high end sound. My primary issue is what device can serve as the pure digital source that connects these devices to and send the AES XLR to the 7270a?

Dan
ilkka-rissanen, modified 5 Years ago.

Re: Digital monitoring control with 82xx/72xx series

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
It is typically only professional products that offer true AES/EBU output, but also toslink and coaxial digital outputs can be connected to the digital inputs with certain limitations. Toslink/optical signal needs to be converted to coaxial and the cable length from source to the first device needs to be less than 2 meters. If longer distances are required, an impedance transformer should be used. This topic has been discussed here several times and suitable devices have also been listed. Please use the search function.