Okto DAC8 update with DSP

[fabriceo]

Hi
From a request of @montyliam, here is an example for 6 channel bass management which gives possibility to offload this from JRiver as an example.
Playing with delays on each channels gives the possibility to better align phase shift between SUB and other speaker to minimize excess or cancellation depending on the difference between Lowpass applied on LFE vs crossover frequency applied on the mains channels.
The best is to adjust all of this with mic measurement in the room for each channel instead of developing too much theory
The file is also on the AVDSP_DAC8 GitHub in folder users_examples.

 

[montyliam]

I will be trying this code this coming weekend and will report back with results.

The low down is that using a 120hz LPF on the LFE channel will result in some cancellation between the LFE channel and re-directed bass managed content from the main channels if the main channels -> subwoofer crossover is below 120hz. Thankfully for my system, I usually use a 120hz crossover between mains and subs anyway, so there should be no interaction/cancellation/summation between the two different slopes. If for example, I was to use an 80hz crossover between mains and subs and a 120hz LPF for the LFE, there would be an approximate 1.5db hump at 100hz due to the interaction between the two different slopes.

To combat this, one can use either an all-pass filter on the main channels or a calculated delay on the main channels to bring the phase of the main slopes and the LFE slopes in line. The latter method is preferred due to the increase in group-delay when using APFs.

There is also a third, more complicated method to deal with this issue which it is reported Genelec uses. That is, set the LPF of the LFE channel and the crossover from subs -> mains as the same, and redirect any content above the LPF for LFE to the center channel. For example, using an 80hz crossover all around, the sub only ever receives up to the filter, the main channels undergo the normal bass management and the centre receives the extra content from 80-120hz from the LFE channel. Arguably, a LPF for LFE would not be needed if sending content to the centre, but many have reported that there is esentially some 'artefacts/garbage' above the usual 120hz LPF cutoff for the LFE channel which when not using a LPF can become distracting.

Thank you very much for your help Fabrice.

https://www.aes.org/technical/documentDownloads.cfm?docID=248

 

[montyliam]

Pleased to add I've got the bass management document from Fabrice uploaded and working like a treat. There were a few hicups on the way, namely with the Special USB VID: ID section which caused the Okto to stop recognising USB connection. This was solved by doing a hard reboot of the Okto and it worked perfectly again afterwards. I will perform some more extensive testing with REW loopback soon but so far so good. The only problem I have identified which I have contacted Fabrice about is that the channel delay seems to be limited to 1ms for some reason. This isn't much use when subwoofers are involved when delays reach multiple ms so I'm hoping there is a fix for this. It seems much more stable running this directly from Tidal now rather than Tidal -> WDM -> JRiver -> DSP -> Okto.

 

[montyliam]

First off, I just wanted to say a massive thanks to @fabriceo . He has been a great help and guide throughout the process, and managed to quickly resolve any issues I had/found. The software works great. The process for implementing the dsp program to the DAC is quick once you get used to it, but can be a little tedious to do and I encountered a few problems early on when the DAC would not recognise USB input at all and had to be unplugged and replugged to work again. For some reason, and I don’t know why because the firmware has remained the same, I use the dsp program loading routine often, and no longer encounter the issue above. I would say once you understand the file format, it’s very quick and easy to implement changes based on measured responses in REW. I use MMM to generate PEQ filters between 80-500hz for the main channels where needed. MMM for the LFE. And a single point measurement at the MLP for mains and LFE to determine delays. All of this is used with the Harman Curve profile importable into REW, which I think sounds especially good in a small room like mine.

I was originally doing the room correction ETC in JRiver and using the WDM driver for Tidal. I had heard a few pops and clicks occasionally from this setup with a latency of 100ms. With the room correction now in the Okto, it connects directly to the app using it AKA Tidal or JRiver for films and TV. There are now no pops or clicks of any kind with a latency of 20ms.

Although a slight process, it is worth it for any Okto DAC owners using Jriver to EQ.