# Change X-over on sub channel in HDMI ASIO output



## sveinse (Apr 4, 2008)

I'm using ASIO with REW to access 5.1 using HDMI output. However, the LFE channel seems to be set at a fixed x-over frequency and rolls off around 60 Hz. The other channels playback fine with full bandwidth. I tried googling this, but apparently few has raised this question.

Does anyone happen to know if this can be changed somewhere, or if this is hardcoded into some driver?


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## JohnM (Apr 11, 2006)

Most likely in the processor, the LFE low pass setting is sometimes adjustable in the processor's menus, default is usually 80 Hz.


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## sveinse (Apr 4, 2008)

No, I'm sure it's not. Changing the receiver setting has no effect in the x-over applied by windows. E.g setting x-over in receiver to 160 Hz, still makes the LFE channel roll of starting at 60 Hz.

The unfortunate thing about this is that I cannot use the LFE channel in HDMI with ASIO to measure sub-response over around 60-80 Hz.


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## JohnM (Apr 11, 2006)

The processor has two crossover frequencies, one for bass management (the one you have been adjusting) and another which is a low pass filter rather than a crossover which is applied to the content in the LFE channel. The LFE low pass setting is only adjustable in some processors, it is usually fixed at 80 Hz if not adjustable. 

You could connect the sub to another output temporarily to make measurements, e.g. the centre channel.


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## sveinse (Apr 4, 2008)

Intriguing explanation so I made some tests to see how my receiver behaves. The basic objective is to determine if the receiver/processor sets a non-adjustable x-over on the LFE channel, or if this is done in the PC generating the PCM on the HDMI out.

From a previous development project, I have a set of technical Dolby Digital test vectors. I'm using one vector which contains the full LFE frequency spectrum, that is from 0 to 120 Hz. It is played from a Oppo BDP-103 which is plugged into a Yamaha RX-A1020 receiver. I tested using both LPCM and bitstream. I use the REW RTA to see the spectrum coming out from my LFE receiver output. I then change the X-over setting in the receiver to see if this affects the resulting spectrum.

This is what I have observed:

1) The LFE output plays back the full contents (up to 120Hz) regardless of the X-over setting in the receiver. The X-over is ONLY for setting the X-over between the main speakers and the Sub.

2) It does not matter if the DD decode is made in the receiver (transferred as bitstream in HDMI) or in the Oppo (transferred as LPCM) to the receiver.

The conclusion have to be that this proves that it is Windows that applies a X-over filter on the LFE channel, NOT the receiver. This is proved by the fact that a source other than PC, is able to play back contents on the LFE channel up to 120Hz, but the Windows HDMI LFE is cutting off at around 60Hz.

Hence my initial question still remains: How can I change this X-over frequency? Is it fixed/hardcoded or is it customisable?


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## JohnM (Apr 11, 2006)

Interesting. Which version of Windows are you running? If Win 7 or Win 8/8.1 any audio processing should be on the Enhancements tab of the audio properties of the output, along with a check box to disable all enhancements (right click the volume icon in the system tray bottom right corner, select playback devices, select your output device and click Properties). ASIO would ordinarily bypass all Windows audio processing, but if you are using ASIO4All it is a pseudo-ASIO generated from the Windows streams.


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## ihopethiswillfi (Aug 23, 2014)

i can confirm this. i use w7 x64 with asio4all over hdmi, and a 3.1 set hooked to a yamaha avr.

when i measure speaker 1.4 with rew, which is my sub, the measurements are always exactly the same, irrelevant of the XO set by the AVR.

my solution to measure the sub incl the correct crossover, was to let rew do a fullrange measure of my frontright speaker while it was unplugged. the signal would then only reach the sub with correct XO applied.


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## sveinse (Apr 4, 2008)

I have Win 8.1 and I'm using ASIO4all. I have disabled all enhancements. You have to use the sound setup wizard to get the channel mapping correct. I would assume that this is because windows needs to setup the meta-data on how to setup the PCM link over HDMI. Without you don't get anything except 2 ch PCM. In this wizard you set the number of speakers, configuration and the speaker size. 

I have set all my speakers to large. I am willing to bet that if you set the speaker size to small, they will be x-overed around the same frequency that we are seeing when doing lfe-only scans with REW. So it is this module that I really would like to change the X-over.

Are there other ways to do multi-channel output from the PC and from REW? I mean, I seriously doubt that the display card manufacturer will ever make a low-latency ASIO driver for HDMI.


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## sveinse (Apr 4, 2008)

No updates on this?

Evidently it seems this limitation is not very well known. Perhaps it's not too common to use REW to measure LFE over the HDMI LFE channel then?

I have no clue to which Windows forum to raise the issue. Most is going "80 Hz cross over on LFE channel in HDMI? Eh? cross what?"


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## jtalden (Mar 12, 2009)

If you are measuring the Yamaha LPE output it is highly likely it is applying a standard 80Hz low-pass filter (LPF). 

JohnM mentioned this, and I think he is correct. You can maybe confirm it with Yamaha.

The LPF is only on the LFE channel. It is completely independent of the crossover settings for the mains. I checked the portion of the manual for your receiver for you (Page 100 ± 3 Pages) and found no mention of the LFE LPF. As JohnM explained, if the control is not provided, the value is normally fixed at the 80Hz default value. 

The recording industry guidelines suggest this as the upper limit of program material on the LFE channel. So there is really no need to control this LPF anyway. Moving it lower will only start to remove some of the program material in that channel, and moving it higher will do nothing unless you have an "incorrectly" mastered movie.

Again, If you have main speakers set to crossover to the SW at a higher freq than 80Hz that is no problem. The LPF only impacts the LFE channel, not content from the redirected main speakers.


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## sveinse (Apr 4, 2008)

As I mentioned in #5, I have already ruled out that the Yamaha AVR is applying a fixed/hidden 80 Hz LPF. I proved this by using a Dolby Digital test disc played from my BD-player using PCM over HDMI. This particular test provides full bandwidth (120Hz) pink-noise on the LFE channel. I can then observe that the AVR's LFE output spectrum is full 120Hz, regardless of the AVR X-over setting. The X-over setting ONLY controls the point when the low-end of the other channels are routed to the sub output.

Ergo: The Yamaha AVR will pass the HDMI LFE channel unchanged. Consequently the problem is definitely in the HDMI Source, i.e. the Windows HDMI audio driver.

BTW:
I'd also like to comment that it is a requirement in e.g. the Dolby Digital standard that the LFE shall reproduce sounds up to 120Hz (and then cut off with an 8th order elliptic filter). So subs shall definitely reproduce material up to 120Hz regardless of any X-over frequency in speaker bass management. If content providers actually use the entire 120 Hz bandwidth and have recommendation to set the cutoff lower it is another discussion.


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## jtalden (Mar 12, 2009)

Sorry I tried to bring some practicality to this.


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## sveinse (Apr 4, 2008)

Yes, and thank you for that. I'll just have to search on.


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