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correct way to construct subwoofer channel from 5.1 audio?

Hi all,

A simple question for my first post here on hydrogen. I am working on a tiny music player for linux (my current custom linux based system for playback is 1.5MB, including the kernel). I play back 5.1 audio with this player and was wondering about the correct data to send to the subwoofer. Currently, I only send the LFE channel, but from some reading here on hydrogen that does not seem correct. Is the correct way to construct the subwoofer channel (L+R+C+LFE+SR+SL) / 6 ?

Thanks
Maarten

correct way to construct subwoofer channel from 5.1 audio?

Reply #1
This is called "bass management" and it's not the job of the player.  It's handled at the driver or hardware level. 

The "ideal" home theater system has five full-range speakers plus a subwoofer.  The regular bass in the 5 surround channels goes to the respective full range speakers.  Only the Low Frequency Effects channel goes to the subwoofer.

But, most "real world" home theaters have small surround speakers that can't put-out bass.  So, there is an option on Home Theater Receivers (or with the soundcard utility) that can route the bass from all channels to the subwoofer.

correct way to construct subwoofer channel from 5.1 audio?

Reply #2
I do need to do bass management in the player. My home system does not have full range speakers    I have a receiver, but I use 5.1 channel analog in; as the manual states no processing is done at all in this mode, so I assume also no bass management (which fits with what I hear  For a sound card I have a rme hdsp9632 which, being more of a professional card, does not do stuff like bass management.

correct way to construct subwoofer channel from 5.1 audio?

Reply #3
I do need to do bass management in the player. My home system does not have full range speakers    I have a receiver, but I use 5.1 channel analog in; as the manual states no processing is done at all in this mode, so I assume also no bass management (which fits with what I hear  For a sound card I have a rme hdsp9632 which, being more of a professional card, does not do stuff like bass management.

What kind / brand of receiver is that ? Normally, any selectable bassmgt should be active for this input use case as well.
Apart from that: bassmanagement selfmade for your case (all speakers "small") would mean: the summation of all channels followed by a lowpass for the subwoofer signal, and highpass filters  for all other speaker channels.
Proper attenuation for the summation needed to avoid overload/clipping...don't recall the numbers by heart. 

correct way to construct subwoofer channel from 5.1 audio?

Reply #4
What kind / brand of receiver is that ? Normally, any selectable bassmgt should be active for this input use case as well.
Apart from that: bassmanagement selfmade for your case (all speakers "small") would mean: the summation of all channels followed by a lowpass for the subwoofer signal, and highpass filters  for all other speaker channels.
Proper attenuation for the summation needed to avoid overload/clipping...don't recall the numbers by heart.



Hi,

Thanks for your answer.

The receiver is a Marantz SR5400, this is the manual:
http://us.marantz.com/c_sr5400_man.pdf
From Page 28:

"6.1 CH INPUT.
The SR5400 is equipped for future expansion through the use of Multi channel SACD multichannel player or DVD-Audio player.
When this is selected, the input signals connected to the L(front left), R (front right), CENTER, SL (surround left), SR (surround right) and SB (surround back) channels of the 6.1 CH. In jacks are output directly to the front (left and right), center, surround (left and right) and surround back speaker systems as well as the pre-out jacks without passing through the surround circuitry. In addition, the signal input to the SW (subwoofer) jack is output to the PRE OUT SW (subwoofer) jack."

Which I assume also means no bass management. From page 26 in the manual there does not seem to be any (other) surround mode which works with all channels on analog input.


I am mixing all 6 channels together attanuated by a factor 6 for the subwoofer channel. I don't have low or high pass filters implemented (yet). The subwoofer has a low pass filter built in, but I can see it would be better to high pass the other speakers. I guess that does away with nice low latency hardware mixing in the RME card. I might also have to get the processor to run a bit faster 
(I am using a fanless pc with a via c7 running at its minimum 400Mhz, it has plenty of power for simple playback of 5.1, 24 bit, 96kHz flac files in a bare bones linux system but don't think it can do filtering of that amount of data)



correct way to construct subwoofer channel from 5.1 audio?

Reply #5
The receiver is a Marantz SR5400, this is the manual:
http://us.marantz.com/c_sr5400_man.pdf
From Page 28:

Which I assume also means no bass management. From page 26 in the manual there does not seem to be any (other) surround mode which works with all channels on analog input.


I am mixing all 6 channels together attanuated by a factor 6 for the subwoofer channel. I don't have low or high pass filters implemented (yet). The subwoofer has a low pass filter built in, but I can see it would be better to high pass the other speakers. I guess that does away with nice low latency hardware mixing in the RME card. I might also have to get the processor to run a bit faster 
(I am using a fanless pc with a via c7 running at its minimum 400Mhz, it has plenty of power for simple playback of 5.1, 24 bit, 96kHz flac files in a bare bones linux system but don't think it can do filtering of that amount of data)


Weird statement about the analog mc inputs. I'd still would give a shot though, that is in the setup menu, set all speakers to
small, subwoofer to yes and try...if no bassmgt happens, that is worth a complaint at marantz (which wouldn't solve
your problem either...).
Regarding the filters: they are often simple 2nd order biquads (IIR), and don't came that expensive in terms of
cycle count and memory.
Good luck with your project..

 
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