| Read this article for understanding more about the
waveplay-devices, the virtual channels, and the limitations of the ISA bus. How much do you
ask from your system? Two types of Virtual Channels
Theoretically the EWS64 has two types of virtual channels (=wave playback device):
logical and physical. Each of the wave output devices (8 in default) uses one logical
virtual channel. Each application that opens a wave output uses one physical virtual
channel (vc).
The EWS64 firmware has implemented 32 vc's and you can select under properties of the
synth in control panel how much of them you want to assign to a wave output device (8 in
default). However, you can however use up to 32 vc's, even if you don't have enabled all
32 devices. This may happen since a wave output device can be opened by more than one
application at the same time. You can try this by double-clicking on a wave-file in the
explorer and then double-click on another file while the first one is still playing. The
two waveforms are mixed together by the firmware (=hardware mixing) and played together.
With most other soundcards you would get a error msg when clicking on the second file.
This also works even if you only assigned one single playback device. So: up to
(theoretically) 32 applications can open one device at the same time if no other device is
oppend. All together not more than output devices can't be opened more than 32 times at
the same time. It's hard to describe but I hope you did get it ...
The way the EWS64 mixes these wave streams together is called 'hardware mixing' and is
advertised as one of the features of the card (=the soundcard is mixing the stuff from the
devices within the DSP to one output signal). The problem is, that this sounds
theoretically very good, even excellent, but it also has some hard limitations.
The alternative is to use only one single device (like you would do with a normal
soundcard). As the device is not able to mix different wave streams (it is opened only one
single time!), the playing software (CoolEdit Pro, Cubase, Cakewalk, Samplitude, SAW,
etc.) needs to perform this task. This is made differently by different software. Normally
in memory of the PC or directly on the harddisk (=the software mixes the stuff to one
single wave which is played afterwards).
If you compare these two methods you may think (of course!) that the first one is better
since it does not use as much CPU power and since it is able to reduce the latency on
playback (harddiskmixing takes time).
The ISA bottleneck
The problem that now appears is not the soundcard or the driver. It's the PC itself, or
better: it's the ISA-Bus. The data-transfer rate on the ISA-Bus (where you placed your
EWS) is limited. If you are using more than one device at the same time and the stuff
needs to be mixed within the DSP on the card (hardware mixing) this also means that the
wave-data of all tracks you are playing needs to go through the ISA-Bus. If the
transfer-rate needs to be higher you are getting timing problems. On most mainboards this
will happen somewhere between 5 or 7 tracks - with some luck you can play 8 tracks
(depends on BIOS settings, the chipset, etc.).
When using software mixing (with higher latency of course), this won't appear because only
one wave stream needs to go through ISA-Bus to the soundcard. However, if the software
performs harddisk mixing (like Cubase and Samplitude for example) the data of the streams
goes to the harddisk. So if you have a slower harddisk (or you're using an older ISA
controller) you won't be able to play as much tracks as with hardware mixing. If the
transferrate is high enough, you will be able to play more tracks at the same time but
with a higher latency (only a bit normally).
It will be TerraTec's secret forever I guess why they did invent 32 virtual channels. The
original Dream firmware has 8 vc's (and that's even a bit more optimistic than just
realistic).
The only solution to solve this problem is (sounds hard...): PCI. |
