Foobar Convolver Plugin

Been checking out a friends Windows Media Center for a while now. Decided to start my venture into the PC audio arena by resurrecting an old desktop system as a music server for my garage/shop office.

A little about the equipment - I totally believe in isolation from desktop internals for my gear so with that, for ripping audio I have an external Plextor Premium-U (USB 2) CD writer and use Plextools Professional (error logging) for the DAE process to PCM format. The sound card is integral to the motherboard - NFG. My Media Center buddy went on vacation this week so he was nice enough to loan me his Waveterminal U24 USB sound card and a DIY TDA1543 non-oversampling DAC for me to play with (sounds great by the way in his system). So here's the rig:

PCM files > WMP9 > Waveterminal > SPDIF > DAC > Hafler SE120/100 amp/pre > Ohm H speakers

Sound is very good, but at times a little bright. I tried fiddling with the U24 control panel but any changes I made left me with either polluted or no sound at all. Decided to try a different player. I kept reading about Foobar and it's exceptional playback qualities and decided to give it a try. Big mistake - I like to tweak. Anyhow, I didn't realize any difference whatsoever between WMP9 and Foobar to my ears. Tried Foobar in waveout, kernel streaming and direct sound modes ( I did find an ASIO plugin that I haven't tried yet). I do like the open source and clean/low overhead aspects of Foobar though. Got to poking around and noticed the DSP manager and started looking into that when I came across the "convolver" plugin. Apparently with this plugin you can use "impulse" samples (waveform signatures?) to model other waveforms to it. Poking around some more I found impulses which model rooms, halls, cathedrals, auditoriums, guitar amps, microphones, etc. Found a great number of them here . More searching led me to a download of which contains a number of "tube-like" impulses. This one caught my attention. I installed the convolver plugin and started playing with the samples. Interesting effects on the sound to say the least! Of all the ones I have tried the "SPL GoldMike Impulse" has had the most pleasing effect on the sound - with no apparant degredation. I may be on to something.

Interesting little find (for me anyway). Considering the concept, one would believe that perhaps impulses of extremely high-end reference equipment could be created and applied in this manner. I'm sure you could never replicate the purity of good gear but by utilizing this method one could almost stumble upon an excellent sounding setup. Not quite sure that I have done things completely right in my testing. Seems to me that in order to do PC Audio right, there is initially some considerable investment in an external sound card and DAC. Seems absurd that I would have to ultimately "fix" the sound with software.

Of course, I am very new to the PC Audio concept. Would appreciate input from some of the veterans to critique my setup. Also some thoughts and opinions if any of you have spent any time with the convolver plugin, which in my opinion is the most intriguing element of my experimenting so far.
Slothman, have you tried the U24's inner DAC by simply taking the analog outs from the U24 into the preamp without SPDIF conversion? I'd really like to know, if you did, how it compares to the current SPDIF set-up - I'm looking to buy a Waveterminal and was lead to believe that it sounds reasonably good by itself.
Vdeakin -
I'll pickup some adapter plugs, 1/4" phone to RCA at the Shack today and try it out. Looks like this U24 is more of a musicians item.
Gotta like snowdays in the great Northeast!

OK, picked up the adapter plugs at RS. Stopped by my local PC boneyard and what do I find? A bloated, scotch-taped box containing a Xitel Pro HiFi-Link (and cables!) for $10. Excuse me while I finish laughing. Anyhow, time to get serious about this little exercise. I felt I really needed to do some sound comparisons with these "magic boxes" so I decided to move the show back into the house and use my home system CD player as my reference, utilizing what I consider my better gear and cabling as well as the convenience of my laptop.

First thing I did was hookup the Plextor and ripped three cuts that I thought would be the most challenging and convincing for the test:

• Cassandra Wilson - New Moon Daughter - Track 1, Strange Fruit
Vocals, challenging bass and my man Chris Whitley's raunchy and exclamatory National Steel riffs

• Pat Travers - Crash and Burn - Track 4, Born Under a Bad Sign
The drums are well recorded on this cut, nice, tight bass punch and well defined cymbals. I chose this cut primarily because of this.

• Jorma Kaukonen - Blue Country Heart - Track 4, Red River Blues
Acoustic - bass, guitars, banjos, mandolins - all kinds of stuff going on here - some crisp and taxing highs

Here's the setup. Far from reference equipment. This is a very recent system (except for the speakers) and I am extremely pleased with it. The amps are running in triode mode and connected to the passive outputs of the preamp - no tone controls. In keeping with the subject of the thread, I evaluated using the Foobar player only. I also decided to take the external DAC out of the equation and just evaluate the U24/Xitel on its own. To demo, I would cue up the track in the CDP and the corresponding PCM track in Foobar. I would start the CDP and then 10 seconds later, start the track in Foobar, listening to the "reference" first and then switch over and listen to the same passage through Foobar and the device being tested.

PCM files > Foobar2000 > Waveterminal/Xitel/Adcom GCD-700 CDP > Adcom GFP-565 Pre-amp > Rogue M-120 Monoblocks > JBL L100T Speakers (1986 vintage)

I started the tests initially without the Foobar convolver plugin initialized. I spent some time determining which output mode was best for each device. Long story short, I found that the Xitel worked best with DirectSound v2. I then installed the ASIO plugin and used the ASIO drivers for the U24 to get it out of Windows control. Determined that ASIO output was best for the U24. I also had to raise the replay gain in the playback settings 3 db to match the level of my CDP.

• Xitel - I was amazed at the sound I was getting through this inexpensive device. Compared to the Adcom the sound was on the bright side with the highs a little washed out and the mids a little grainy. Bass was slightly muddied and lacked the punch of the Adcom. Although the differences were noticable, I spent a good hour with the Xitel listening to the test tracks and did not find it too fatiguing. My overall summary is that it was just a little too bright.

• U24 - This device kept right up with the Adcom. Very good sound. The bass was solid and the highs were crisp and contained however it was slightly less dynamic in the mids, especially with vocals.

Now, on to the convolver plugin. I found a number of these impulse files at The ones that I used most were: collection located at collection located at

Of all the impulses I played with so far, the ones that I found had the most pleasing and noticeable effect on the sound were:

• neutral.wav
• SPL TubeVitalizer Impulse Soft 2xLCFilter.wav
• SPL GoldMike Impulse.wav

I tested these three impulses on each device with excellent results. Again, playback levels had to be matched to the Adcom with each impulse installed. Only this time the levels were raised 3 db by adjusting the plugin parameters and checking the "auto level adjust" box as well.

• neutral.wav - this impulse had very little effect with the U24. If anything, it tightened up on everything ever so slightly - sort of brought the ceiling down just a bit. Effectively rolled the highs back and reduced the graininess on the Xitel, however did nothing to help the bass.

• SPL TubeVitalizer Impulse Soft 2xLCFilter.wav - this impulse rolled the highs back a bit and boosted the bass on both cards with the greatest difference being observed on the Xitel. I found this impulse to be the best for use with the Xitel.

• SPL GoldMike Impulse.wav - this impulse proved to be the dynamics equalizer for the U24. Head to head with the Adcom, I could notice absolutely no difference with the U24 playing the same track - across the board. Improved dynamics with the Xitel as well, however I found the previous impulse to be better suited for this device.

Conclusions. The U24 Waveterminal proves to me that the possibility of using a PC-based "transport" is certainly a sonically acceptable option with my home system. With a little software tweaking, it sounds as good as my Adcom player. Of course there are many CD players out there that would blow my Adcom away. From what I have seen on the net, some $70 dvd players could do that as well. Perhaps I haven't proved very much to myself. I do know that for $10, this little Xitel gets me into the game quite "good enough" for my shop system. Meanwhile, I'll sit back and maybe stumble upon a U24 cheap while the advancements continue.

The neat thing is that in the realm of PC audio, some excellent "tweaks" can be made at a software level - much better than throwing a couple hundred bucks at a cable or something that might gain you similar improvement. Anyhow, I'll stick with my cheap Xitel and free Foobar software and plugins for now and see how things develop. Even though I'm new to this and have done limited experimenting, I thought I might just as well share my experience so far with the group. Would be interested in hearing of other experiences with the convolver plugin should anyone else try these impulses. Have fun!
Well done, Slothman.
If I may continue a little longer as a self-appointed inspiring muse... it's been mentioned on (look for John Swenson in PC AUDIO forum)... to make it short, he's disconnected the voltage wires (#1 and #4, if I'm not mistaken) of the USB bus in a similar device (some Edirol) after taking it apart and replaced them with a 5 or 6 volt battery - he was plain astounded by the improvement. This could be done with either Xitel or Waveterminal.
BTW, U24 has just been discounted by 30% and can be had for $160.00.
Also, I was wondering (and, maybe, I'm plain ignorant here) if you could eliminate the preamp from the chain, I couldn't tell whether you've adjusted the playback settings by 3 db on the computer side or on the preamp. If it's the former, then maybe you could go into the amp directly. You can certainly try it regardless - there is a volume control on the PC.
I've never heard of Xitel, and, as I was looking it up, I've noticed that they supply 30' cables, which could have a negative effect, though I doubt that you've been using them.

Thanks again for clarifying the U24 qualities - I think I'm going to get it.
Meanwhile, keep us posted.

I increased the levels for the Xitel/U24 within the Foobar software. Turns out, however, that the Adcom CDP has a set of variable output connectors - I could have made the level adjustment by bringing down the CDP with the remote to match the devices. Guess I could have hooked it up that way, but the software control was just too easy - hence the term "Slothman". Also, going through the preamp with both devices allowed for efficient switching between the Adcom CDP and the Xitel/U24. By the way, I was using quality IC's( the one's that came with the Xitel I will use in my shop system.

I'm pretty sure I could hook the Xitel up directly to my M-120's and control volume through Windows. Unless I'm missing something, the U24 is a different animal. The control panel provided by the U24 driver is maxed out at 0db by default. Volume control is greyed out in Windows and using the ASIO plugin, there is no direct volume control in Foobar other than increasing the gain in the playback control as mentioned before.

I just looked at some posts on audioasylum concerning the Xitel - turns out that it upsamples to 48hz which may be the cause of its brightness. I had the U24 locked in a 44.1hz in my tests. I'll see what I can do about trying out the U24 directly into my amps. We've been getting dumped on here in Maine and the girlfriend is looking to get out of Dodge tommorrow for an extended weekend - little bit of cabin fever. I'll get back to you on that one. By the way, I hadn't paid much mind to the variable outputs on the Adcom CDP until you sort of reminded me. Looking forward to listening to that directly through the M-120's as well. I'll look into that battery mod also - might be something I'd be willing to try on the Xitel but I don't think my buddy would appreciate it on his U24.
Perhaps a testament to the Adcom preamp but the CDP/Xitel/U24 appear to all have the same sonic delivery whether they are running though the preamp (bypassing tone controls) or directly to my M-120's.

Had to give back the U24 today. My buddy is going to try Foobar and my convolver impulses and see what it does for him. I will say that I am impressed with the U24's performance as an acceptable solution for tying PC audio into my home system. For now I will continue through my learning curve with the Xitel.
you should try to pick-up an Edirol UA-5 used. This has external power, coax out, a driver that supports 24/96 and avoids Kmixer. I recently modded the UA-25 (which is similar) to add coax out, external power and Superclock and it performs superbly.