Motu 8A Measurements

[zeb512]

I'm using a Motu 8A because of your post and very happy with it but I'm not sure how to configure output trim...
Any help will be appreciated:

I've two channels to Sabaj A20A with XLR and one channel with RCA to my Sub (with TRS to RCA cable)
From the Motu 8A documentation: Max level: +20 dBu (range -4 to +20)

So my understanding it that setting the trim to 0 I will have +20dbu.
To go to +4dbu i've set the R and L channel to -16.

My question is how to set the trim for the Sub to compensate to +4dbu an then attenuate again to go to -10dbv ?

 

[zeb512]

I'm using a Motu 8A because of your post and very happy with it but I'm not sure how to configure output trim...
Any help will be appreciated:

I've two channels to Sabaj A20A with XLR and one channel with RCA to my Sub (with TRS to RCA cable)
From the Motu 8A documentation: Max level: +20 dBu (range -4 to +20)

So my understanding it that setting the trim to 0 I will have +20dbu.
To go to +4dbu i've set the R and L channel to -16.

My question is how to set the trim for the Sub to compensate to +4dbu an then attenuate again to go to -10dbv ?

Is my reasoning fine if I target 0.32V * 2 has I have half the signal due to the TRS to RCA cable so around -2dBu.
It will end up with -16 on the Amp side and -22 (-16 and -6) on the Sub channel.
Is there something I've missed ?

 

[mdsimon2]

Is my reasoning fine if I target 0.32V * 2 has I have half the signal due to the TRS to RCA cable so around -2dBu.
It will end up with -16 on the Amp side and -22 (-16 and -6) on the Sub channel.
Is there something I've missed ?

Your math looks correct to me.

For the amp you are starting with +20 dBu or 10^(20/20) x 0.775 = 7.75 V. Attenuating by 16 dB gives you +4 dBu. As a sanity check 7.75 V x 10^(-16/20) = 1.23 V which is +4 dBu.

For the sub using TRS to RCA will reduce your level by half (6 dB). So your starting point is +14 dBu or 10^(14/20) x 0.775 = 3.88 V. Converting dBu to dBV is just dBV - 2.2 so your starting point in dBV is 14 - 2.2 = 11.8 dBV, therefore to end up at -10 dBV you need to attenuate by 11.8 - (-10) = 21.8 dB. As a sanity check 3.88 x 10^(-21.8/20) = 0.32 V which is -10 dBV.

Michael

 

[zeb512]

Your math looks correct to me.

For the amp you are starting with +20 dBu or 10^(20/20) x 0.775 = 7.75 V. Attenuating by 16 dB gives you +4 dBu. As a sanity check 7.75 V x 10^(-16/20) = 1.23 V which is +4 dBu.

For the sub using TRS to RCA will reduce your level by half (6 dB). So your starting point is +14 dBu or 10^(14/20) x 0.775 = 3.88 V. Converting dBu to dBV is just dBV - 2.2 so your starting point in dBV is 14 - 2.2 = 11.8 dBV, therefore to end up at -10 dBV you need to attenuate by 11.8 - (-10) = 21.8 dB. As a sanity check 3.88 x 10^(-21.8/20) = 0.32 V which is -10 dBV.

Michael

Thanks

 

[Deleted member 4708]

I use the 8A to apply 10 point PEQ to all my heaphones: as per https://www.reddit.com/r/oratory1990/wiki/index/list_of_presets/
You can apply only 4 PEQ points per pass so you have to route back into mixer 2 more times to get 12 points.
I use "group sends" for each one of my headphone such that I can choose between the phones by switching the group that is monitored.

This is just one example how powerful the 8A interface is, Very slick and very elegant. Given the rich IO and all the features I believe it is worth the money.

I also use the 8A from a fanless HTPC to drive the Benchmark AHB2 => Perlisten S7T and intend to keep this configuration.

 

[Deleted member 4708]

Update: I figured out how to mix 5.1 to stereo using MOTU 8A. Split center, split bass and everything else goes naturally (front left and back left => left, the same for right).
The only limit with MOTU 8A is your own imagination.

 

[dped90]

Yes I have three interfaces. I've posted some measures of a Focusrite 18i20 here.
https://audiosciencereview.com/forum/index.php?threads/focusrite-18i20-dac-measurements.2128/

Mine is a gen 1 unit, gen 2 units are similar using same chipsets only they work at 192 khz instead of only 96 khz.

I also have an Antelope Zen Tour and Focusrite Forte. The Forte is mainly the ADC/DAC chips and circuitry that is in the Focusrite Clarrett series. Both of those have better measured performance than the 18i20. In time I can post some measures of the other interfaces. I think if people were aware that generally prosumer or pro audio gear performs closer to spec than lots of consumer gear there would be wider use of it by audiophiles. The main thing lacking is remote control. Though many newer interfaces allow remote control via phone apps.

You really nailed one of the three biggest problems audiophiles have with pro audio MCH DACs: No volume/mute remote! Actually, the MOTU 8A is the only pro or consumer 8 channel DAC I've found, save for the Exasound and Okto consumer DACs, where at least there's a phone app remote. But my current problems with building my hopelessly overdue 5.3 system also stemmed from pro audio MCH converters with way more than the 8 channels I need, no USB audio input and/or insufficient balanced output voltage/channel to offset DIRAC room correction software losses.

But so far it looks like the MOTU 8A has all of that covered. Specs show it does 20 dbu https://motu.com/products/avb/8a/specs.html , or ~ 7.8 volts/channel max. https://www.sowter.co.uk/decibels.php , which depending on amplifier input sensitivity, speaker efficiency, room size and listening volume may be enough to offset DIRAC gain losses.

I just wish that MOTU and more pro audio converter brands would follow Prism's lead to offer customers options to omit ADCs and connectivity lots of audiophiles have no use for-and certainly don't like paying for, and other "prosumer" DAC options. The pro audio market should realize that lots of audiophiles prefer high performance "straight" MCH DACs to the "all in one" processors, however well designed (Marantz, Anthem, Lyngdorf, Trinnov, Audio Control, Theta Digital), but which both measure and sound superbly to most ears. And converters designed with enough versatility to permit more customizable options.

The price of MOTU 8A is like 1/6 of my budget for an 8 channel DAC with all required features. Needless to say, if I can confirm with MOTU Support that it meets all criteria I'd gladly go with it. But please recommend any alternatives which might prove far better. Aside from DAC performance, my biggest signal quality concern is loss of resolution from digital volume or level controls, remote or otherwise.