• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Review and Measurements of Okto DAC8 8Ch DAC & Amp

Just for me to understand as I have never used a RME unit. You mention an ADC, is that a separate box or the ADC in the RME? Is the SPDIF loop-back internal in the RME or did you connect SPDIF out to in, by cable on the RME. Or was the loop-back done in a separate box? If so, what was that?

I understand that SPDIF and AES are in principle the same save for the voltage level and one "control bit". The signal fed to the Okto was that SPDIF or AES and if SPDIF from the RME was is the same signal as the loop-back?

The RME is an interface with lots of analog and digital I/O, see here for more info -> https://archiv.rme-audio.de/en/products/fireface_800.php. A rough sketch of the hardware setup is shown below.

1736176213583.png


In this case I have the RME mixer set so that when I play to channel 1/2 it outputs to both the optical and coaxial SPDIF outputs. RME coaxial SPDIF output is AES compatible and is connected to the Okto via a coaxial to XLR cable to AES input 1-2. RME optical SPDIF output is routed to the RME optical input for use as a timing reference. Okto analog output 1 is routed to RME analog input 1 for use as the main measurement channel. In REW the left channel is used as the main measurement channel and the right channel is used as the timing reference.

Sorry for all the questions but since I'm mixing two different DAC's in the same system understanding why I got +2ms and you got 1,23ms is important in my system. I need to delay my other DAC's to compensate for the Okto latecy. And gain.

Important to note that the setup describe above was an attempt to quantify worst case absolute latency of the Okto. If I wanted to use the Okto in a system in conjunction with the RME analog output and wanted to determine relative latency between the Okto and RME analog outputs, I would have used the analog output of the RME as a timing reference, not the SPDIF output.

Can you please check levels also, ie what is the level out, at 100% volume, compared to input. Just a compare measure would be great. My finding of +5db sounds high.

I get 4.3 V from the Okto when fed a 0 dBFS sine at 100% volume.

A few questions for you. From your description you are sending an analog signal to the BSS, what specific hardware are you using to do this? I assume that this device also has an ADC that you are using for measurements? I assume your measurements are electrical, not acoustic via a microphone? What specific BSS DSP are you using?

Michael
 
Great.

Now even I understand. Thank you.

A bit puzzling as that is kind of the same as I did. I fed the BSS a digital MLS signal via SPDIF and from there the internal DAC's and also Okto digital AES signal from the BSS digital output card (can chose SPDIF or AES out). I then compared to the Okto analogue output to the analogue output from the BSS analogue output card = DAC. As the BSS always time all outputs I'm pretty sure that the digital out (to the Okto) and the analogue output from the BSS are in sync, hence the delta would be the latency of the Okto. Same as you. Kind of.

But as mentioned +2ms sounds high and your measurements are probably right. I need to figure out where my setup goes wrong.

Your setup should give very precise data with the carve out regarding any potential timing differences between Toslink and coax SPDIF in/out. Probably completely neglectable.

Good news.

I am feeding the BSS digital signal via SPDIF in, so there are no ADC in the signal path until the DAC's (8-channels) in the BSS and the Okto DAC (8-channels).

Not sure what 0 dbFS in being 4,3V out means in the form of attenuation, if any? Can you please elaborate? I'm reasonable good at acoustics & analogue but less so in the digital domain. :)

If you compare the analogue output of the RME with the analogue of the Okto (AES in) using the same signal, is there a difference there?

Kind regards and thank you
//Robert
 
I then compared to the Okto analogue output to the analogue output from the BSS analogue output card = DAC.

How are you doing this comparison? I assume you need a dual channel ADC somewhere to make this comparison, hence my question about the ADC.

Not sure what 0 dbFS in being 4,3V out means in the form of attenuation, if any? Can you please elaborate? I'm reasonable good at acoustics & analogue but less so in the digital domain. :)

If you compare the analogue output of the RME with the analogue of the Okto (AES in) using the same signal, is there a difference there?

This is the point that we've been trying to make to you. DACs have different maximum output levels, this does not mean that a particular DAC is attenuating a signal, just that the maximum output level is different.

My Okto has a maximum output level of 4.3 V, whether or not that level is higher or lower than the maximum output level of another device entirely depends on the maximum output level of the other device. The RME for example has 3 possible settings for maximum output level (+19 dBu, +13 dBu, +2 dBV). The Okto maximum level compared to the RME maximum level for each setting is shown below.

+19 dBu (6.90 V): 20 * log(4.30/6.90) = -4.1 dB
+13 dBu (3.46 V): 20 * log (4.30/3.46) = +1.9 dB
+2 dBV (1.26 V): 20 * log (4.30/1.26) = +10.7 dB

This is why I want to know the specific hardware you are using, so I can know what the maximum output level is.

Michael
 
How are you doing this comparison? I assume you need a dual channel ADC somewhere to make this comparison, hence my question about the ADC.



This is the point that we've been trying to make to you. DACs have different maximum output levels, this does not mean that a particular DAC is attenuating a signal, just that the maximum output level is different.

My Okto has a maximum output level of 4.3 V, whether or not that level is higher or lower than the maximum output level of another device entirely depends on the maximum output level of the other device. The RME for example has 3 possible settings for maximum output level (+19 dBu, +13 dBu, +2 dBV). The Okto maximum level compared to the RME maximum level for each setting is shown below.

+19 dBu (6.90 V): 20 * log(4.30/6.90) = -4.1 dB
+13 dBu (3.46 V): 20 * log (4.30/3.46) = +1.9 dB
+2 dBV (1.26 V): 20 * log (4.30/1.26) = +10.7 dB

This is why I want to know the specific hardware you are using, so I can know what the maximum output level is.

Michael
@sebackman is using BSS BLU 800 DSP, with different AI/AO, DI/DO cards see attached image

The okto with its 4,3V 14,9dBu

and the BSS 6,9V 19dBu

So in theory it should be a 4,1dB difference
And
If the voltage is 4,2V as the data sheet on a standard okto the difference should be 4,3db
 

Attachments

  • Analog bss.png
    Analog bss.png
    168 KB · Views: 25
  • digital bss.png
    digital bss.png
    119 KB · Views: 26
Last edited:
Hi dualzmak,

That is way above my pay-grade. I my case it is not that complicated as no USB is involved at all.

My system (aktive 3-way (LCR) & 2-way system (rear) 5.2 (+ 2 subbs) = 15 channels used) uses a buildable DSP system (BSS) with the option of analogue and/or digital input and/or output cards. Each card has four channels and one unit hold 4 cards (16 channels). The system can handle up to 128 channels in and out.

The BSS system comprises of a DSP core and user selectable input and/or output cards. Each physical unit can take 4 cards and can be expanded up to 128 channels with additional units/cards. I have two input cards with together 8 channels digital input, 4 analogue output cards, DAC's, (16 channels) of which I use 2 and 2 digital output cards (8 channels) that feed AES to the Okto (8 channel unit).

I feed my DSP unit 7.1 SPDIF 48kHz/24bit digital signal that goes into a sample-rate converter (in the DSP) and into the DSP system. The DSP does its magic in the digital domain (41 bits floating point) and sends 8-channels to 4x 4-channels DAC cards using the same clock (using only 2 cards = 8 channels analogue) and 2x 4-channels digital output cards using and embedding the same clock.

The analogue output from the DAC output cards (8 channels) feeds part of the system and the digital output cards feed the Okto for the rest of the system. The digital output cards can be set to SPDIF or AES and will carry the clock in the signal. The DSP is "smart" and will make sure that all outputs are in sync, ie add latency so all output regardless of SW or HW are in sync. The Okto receives 8-channel AES signal in and, as far as I can understand, picks up the clock from channel 1, which should give a system in clock sync.

What I need to do, as opposed to your system, is to compensate for the Okto latency (AES in to analogue out) compared to the DSP DAC's which are in timing sync with the digital out feeding the Okto.

-And to compensate for the fact that the Okto seem to have some attenuation on the output compared to the input.

Does that make sense?

Kind regards
//Rob

OK, I thank you so much for your detailed description (and you time for writing) of your sync approach in your audio signal chain.

Now I well understand you do have "exact and consistent" sync mechanism by using S/PDIF and/or AES/EBU all the way through in your signal chain which Pavel of OKTO recommends and prefers; it looks he is rather skeptical for sync by outer common clock (10 MHz?) distribution to multiple DAC's.

BTW, if it would be possible at your end, I (we?) would highly appreciate if you could prepare/share a schematic diagram (even hand-drawn diagram should be fine) of your total signal chain for my (our) at-a-glance observation and understanding on your wonderful audio system.
 
Last edited:
Hi dualzmak,

I do understand the gain issue and have discussed with member "beatelund", who is also very helpful. He also seem to come to +5db difference between the Okto and BSS, so that seems reasonable.

I have adopted you latency of 1.23ms and that sound good on a quick test. I need to figure out where my measurement went wrong.

Attached is a simplified description of the sound-part of my system. The pre-amp is just a "digital switch" and with the right parameters it outputs non-encrypted digital 7.1 spdif 24/48 (up to 96). No ADC's in the system except for the turntable.

I do have a HDMI to SPDIF unit that will be implemented the next few weeks and will provide un-compressed 7.1 digital decoded sound from Bluray and similar.

Kind regards and thank you
//Rob
 

Attachments

  • System 2025 01 08.pdf
    76.3 KB · Views: 31
Hi dualzmak,

I do understand the gain issue and have discussed with member "beatelund", who is also very helpful. He also seem to come to +5db difference between the Okto and BSS, so that seems reasonable.

I have adopted you latency of 1.23ms and that sound good on a quick test. I need to figure out where my measurement went wrong.

Attached is a simplified description of the sound-part of my system. The pre-amp is just a "digital switch" and with the right parameters it outputs non-encrypted digital 7.1 spdif 24/48 (up to 96). No ADC's in the system except for the turntable.

I do have a HDMI to SPDIF unit that will be implemented the next few weeks and will provide un-compressed 7.1 digital decoded sound from Bluray and similar.

Kind regards and thank you
//Rob

Thank you indeed for your kind follow-up with nice diagram for my (our) "at-a-glance" understanding!

If acceptable for you, I would highly appreciate and welcome your kind participation on my thread, having your signal path diagram (and hopefully photo of your system).;)
- Let's share diagrams (and photos) of our total physical audio system and the whole signal path, with a few words and/or links
 
Back
Top Bottom