Hello,
I am looking for a cheap soundcard that has the following
features and that is ALSA supported:

- it can record while playing (full-duplex capable, I think
this is the exact term)
- it should have at least one output for headphones and one for
speakers (it should be dj software capable, even in windows, not
only in linux)
- it should have one midi or joystick input to connect a keyboard
and be happy with ardour or other sequencers (to work with ardour
and keyboard I need wavetable synth or not? Please explain me..),
or can I handle usb keyboard to work with ardour? I have a bit
of confusion :-)
- it can record from line in input

Few days ago in another thread someone suggest me creative soundblaster audigy SE. It seems a very good solution, cheap and that can work
up to 96 KHz, but on the ALSA site I see that:

Sound Blaster Audigy SE
Sound Blaster Audigy Value

CA0106
Details [PCI] Digital/Analog input does not work yet. Needs more development work.

So I think I cannot capture from line in, right?
Mmmhhhh, any suggestions?
Thanks,
tano

How about the Creative Labs SB Audigy? Works well here using emu10k1 kernel module.

Exactly,
I think you intend those supported under emu10k2 (platinum, digital entertainment, gamer, es).
However, even if these seems a little dated (there are no refs on creative site), it could be
a solution.
Other possibilities?

Turtle Beach Santa Cruz (hardware mixing)
Audiotrak Prodigy 7.1 (software mixing)

I have both sound cards. Turtle Beach Santa Cruz comes with separate ADC and DAC that helps during duplexing. It has hardware mixing, so no need for dmix. Its sampling rate is limit to 48 KHz and at 16 bit resolution. Audiotrak Prodigy 7.1 does not have hardware mixing so a software mixer such as dmix have to be used. It able to duplex, but only at the same sampling rate that it is playing back.

MIDI can be played through a software sequencer with a lot of control.

I do not recommend Creative Labs sound cards. Yes they may have a reputable name, but they lack honesty in their products and quality of sound is poor.

Probably the best audio DSP chips are VIA ICE1724 and C-Media CMI8788. The VIA ICE1724 has better support in Linux than C-Media CMI8788.

I know that Creative lacks of support for linux, however
I did not found a soundcard with all the features of soundblaster
audigy SE at the same price.
I am looking for solutions that are the cheapest possible, and now
I can look at the chipsets you give me as refs as another element to
evaluate (the fact that via makes hardware good for linux, at least
for audio, is new for me: all the people suggest me to not buy
via chipset on motherboards :-) )

I have looked at audiotrak site and prodigy 7.1 seems to be replaced
by its hi-fi new version. Do you know something about it? Alsa site
does not list an entrty in the audiotrak section. However I search
to vendor if it can be reached the same.

From the ALSA bug reports, the Prodigy HiFi is supported. Also the Prodigy 7.1 LT is supported. The ALSA developers are just lazy to update the list of supported sound cards. It seems to me that the ALSA developers are too busy figuring out a more logical way to provide enough support to snd-hda-intel module which is now the dominate sound module that works with nVidia, Intel, and AMD/ATI motherboard chipsets while keeping up the dramatic changes of the kernel between bug relases of the 2.6.x kernel.

People that recommend to not get VIA motherboard chipsets are idiots because they do not have a reason for their recommendation. My reason is to not mix Creative Lab Soundblaster LIVE and probably above with VIA mainboard chipsets because Soundblaster LIVE is known to change some registers to fix bus fluctuations which cause data corruption. When complying to this rule, you can use a VIA chipset just fine. I have a VIA KX133 motherboard chipset that works with out any problems because I use a Turtle Beach Santa Cruz. A lot of people bought and used EPIA platforms which are created by VIA. Also VIA is coming back with some help from nVidia.

The Creative Labs SB Audigy works brilliantly here on a VIA K8T800 ASUSTeK K8V-X Rev 2.0 mobo (VIA VT8237 onboard audio never used).

Electro is right about a lot of work going into snd-hda-intel. It's getting hard to find a new laptop which doesn't use it.

Essentially all PC's (mobile, desktop) made in the last couple of years and going forward will be using the Intel HD Audio bus specification for on-board audio. It is a replacement to the AC'97 bus definition and is an open specification, so other chipset vendors are implementing the design as well. Device wise, the HD Audio bus shows up as a Class 403 PCI device on most systems. The part that causes the most confusion for users is that they only see Intel HD Audio listed as their audio system. Since this is really just another type of serial bus (very similar to USB, actually), it is easy for manufacturers to add their own audio, modem, and other types of streaming data controllers (currently audio and modems are the only ones using this).

When I last discussed this with a devel, there were eight different vendors and 96 different codecs. To add to the trouble, the HD Audio spec allows each "Pin Node" to be reconfigurable through software. Some are dedicated to a specific task (SPDIF, CD, etc), the rest can be reassigned to either a line in or a line out. To reduce cost, only a couple of nodes have amplifiers for headphones. What ends up happening, is a system integrator (Dell, HP, etc) may decide to buy a specific audio chip for an entire line of systems. Some systems may support only speakers, headphones, and a mic/line-in (standard laptop), whereas other systems using the exact same chip may support up to 8 channels of output (Front, Rear, Sides, Center/LFE, Headphone, Mic). The fun begins when one vendor (Dell) will use a single chip in laptop A wired with Pins ABCD, but in laptop B they use pins EFGH, and in laptop C they use ACFG. The only way we currently have to identify the different configurations is by looking at the PCI subsystem ID and the vendor ID in the codec directly. Even this isn't perfect, as some vendors (Apple) don't define a PCI subsystem ID for the audio device.