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Old 20th November 2003, 10:15 AM   #1
MWP is offline MWP  Australia
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Default BruteFIR / Volume control

Hi all,

How have you guys that have setup BruteFIR filtering box's controlled the volume of the system with multiple channels?

I want to use BruteFIR as an active xover for 3-ways (so, 6 outs), and cant work out what the best method of volume control will be.... using the soundcards volume controls, using BruteFIRs gain settings, or using some kind of external 6chan volume control (multiple pots?).

Thanks.
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Old 20th November 2003, 05:14 PM   #2
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Depends a bit on your soundcard. If it provides a real multichannel mixer, then using that should be OK. My delta 1010 does NOT, and so I can't use this approach. A Revo might support this, though.

Using BruteFIR's gain settings is probably not the best idea in the long run for a couple reasons.

First, it's digital-domain - although it's 'correctly' done, it won't be completely transparent at lower levels. If you carefully match the soundcard output levels to your amp input sensitivity (using a resistive network) this would help a lot.

Second, it would mean wiring your amps directly to the sound card outputs, and would run the risk of sending unattenuated signals directly to the speakers - easy to fry tweeters.

An external volume control would be ideal, but a good 6-channel preamp would be expensive and/or hard to come by. The 6-deck Tact stepped attenuators might be a good approach to look at though.

My digital xo project is on hold right now, but I eventually threw in the towel and just got a HT receiver with a 6.1 input, and tri-amped using that. Works ok, and has 'normal' ergonomics and remote etc. I just got one of the cheap Panny digital units (XR25) as a proof-of-concept, but if you got a good NAD unit for example (762 or the new 763) you wouldn't give up much at all to separate amps.
The XR25/45 might be okay for 'production' use in some cases if you use 2. i think they're great via the digital input, but less so via the analog input. So, use one via digital input for the mids, and the other in analog mode for the bass/tweets. I've verified that a single remote will operate the volume of both in sync, so that's pretty cool.
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Old 21st November 2003, 02:57 AM   #3
MWP is offline MWP  Australia
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Ill probably use a Envy24HT card (modified for 3 TOSLINK outs).

Ill also be build new DACs and Amps for this application.

I might use BruteFIR for the volume control then, and maybe make some kind of external up/down volume control using a printer port interface.

Thanks for the reply.
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Old 21st November 2003, 05:50 PM   #4
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Quote:
Originally posted by MWP
Ill probably use a Envy24HT card (modified for 3 TOSLINK outs).
Have you started concretely designing this, or is it still an idea?
I've looked at various ideas for getting multiple spdif outs, and none are 'easy'. The tight pitch of most Envy24/HT cards makes hacking a bit intimidating. If there is a card out there that is amenable to adding toslink outs, I'd be interested.

Quote:

Ill also be build new DACs and Amps for this application.

I might use BruteFIR for the volume control then, and maybe make some kind of external up/down volume control using a printer port interface.

Thanks for the reply.
Ah, if you're doing custom hardware, then you have some options.

What I'd look at is building 3-4 coarse (10dB) volume steps into either your dac output or amp input, and control them via the parallel port signals. A relay driven resistor array should be pretty straightforward if you are considering DIY dacs/amps.
Use a custom utility (easiest if you're running BruteFIR with Jack, but not essential) to split the volume control between digital-domain in BruteFIR/Jack and the analog steps in the amp. This limits digital domain attenuation to a max of 10dB, which will be completely transparent.
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Old 22nd November 2003, 06:22 AM   #5
MWP is offline MWP  Australia
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Fine pitched stuff has never worried me.
I was thinking about the "Terratec Aureon Sky" card.

Good idea with the volume control... that would work well and would be very easy to setup.
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Old 22nd November 2003, 10:46 AM   #6
Henckel is offline Henckel  Denmark
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Take a look at;

http://www.electricstart.de/

under electronics

for the volumen control take a look at TI PGA 2310

Best regards

Morten
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Old 22nd November 2003, 12:25 PM   #7
MWP is offline MWP  Australia
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Quote:
Originally posted by Henckel
for the volumen control take a look at TI PGA 2310
Yeh, i know about the digital pots.
I would like to stay away from then at the mo, due to them needing a microcontroller to set the volume
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Old 22nd November 2003, 12:46 PM   #8
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Hi!

Quote:
Originally posted by dwk123

Second, it would mean wiring your amps directly to the sound card outputs, and would run the risk of sending unattenuated signals directly to the speakers - easy to fry tweeters.
I've been doing this for almost two years now (two amps connected directly to soundcard output, a mono LCAudio End Millenium and - alternatively - my DIY P3A or GainClone, the GC even without any input coupling), and I had no problems so far.

I only have to ensure to have both amps turned off while switching the computer on or off, since the "POP" of the charging / discharging caps of the soundcard comes out at full power...

Bye,

Arndt
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Old 23rd November 2003, 12:19 AM   #9
agent.5 is offline agent.5  United States
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Take a look at this thread

Found: source for cheap ladder attenuators

Order 3 stereo switchs for 6 channels (or 6 switchs for full differential)

Then put spur gears, or pulleys, on them, connect gears with a timing belt. A multi-channel, differential laddar attenuator is born.
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Old 24th November 2003, 01:39 AM   #10
MWP is offline MWP  Australia
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I also sent an email asking Anders Torger (the guy that wrote BruteFIR) asking the same question, this was his reply:

Quote:
Using BruteFIR's volume controls will mean that the digital signal is scaled.
If you use 24 bit digital outputs to feed your audio system (which you
should), the S/N ratio of the digital signal exceeds any analog system of
today, so the digital scaling should not be problem, especially if dithering
is applied (which it should be).

However, if you are a real HiFi purist, you might want to use external analog
volume controls after the DAC. It is however less practical, and will
probably degrade the signal more than if you let BruteFIR do digital scaling.
Also, the digital signal has been processed anyway, with the crossover
filters.
Sounds good to me....
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