Will Vista ever fully support voice modem based on conexant chip

[Soumen]

I have got myself a Rosewill RC-403 PCI Voice/Data/Fax modem that is not working properly with a number of TAPI based answering machine programs like IVM Answering Attendant, Impulse Technology's CallStation. I can use this programs to pick up record calls but it is unable to play a greeting message over the phone line. The caller only hears silence when the greeting is playing. I was told that there is some bug with Vista's Unimodem Transform Module that affects all Conexant based voice modems. So can anyone help me in this case?

[BoanHed]

This issue cannot be solved with a Driver fix. Device manufacturer's provide with their drivers to microsoft and they dont write any other than their own hardware. So, its upto the device manufacturer to fix or supply the proper version of the driver that will work in the latest operating system. If the device becomes old, then they normally stop updating or making new drivers for same which in the end results in lack of support.

[JUSTICE]

I think that the function of a modem is to give the analog/digital
(modulation/demodulation) exchange of data and it should not support voice modulation. This feature is added sometimes in some of the modems supplied by some manufacturer's. And the driver that is given for the Vista support or any other Windows version allow only the basic functions and not the added features. This thing will only work when the modem manufacturers distributes a supporting driver for this added features.

[Craig Duncan]

I just recently came across this post. As the author of CallStation, maybe I can shed some light on the "voice playback" problem. First, let's do away with some misconceptions.

Some people want to defend Microsoft for some reason, and blame the modem manufacturers for this problem. They think that the drivers are at fault. I can tell you now that this is NOT a driver problem.

Rick Rogers states that Microsoft drivers only provide basic functionality (data/fax), and it is the responsibility of the modem manufacturer to supply drivers which have proper voice support. This is true, and you should always use drivers from the modem manufacturer whenever possible, however, this is NOT the reason for the voice playback problem.

Also, this problem is NOT due to some intentional change in Vista that the modem manufacturers have not yet reacted to. This is a major bug in Vista, plain and simple.

So what is the problem, and why does it mainly affect Conexant based voice modems? To answer that, we need to look at how voice playback works in Windows.

There are two ways that a program can play sound through a voice modem. A program can open the COM port and write data directly to the modem, or it can use the modem wave driver. The problem occurs when trying to use the modem wave driver. The modem wave driver is actually a Windows component.

A voice application like CallStation first has to get a wave-out ID for the modem. It then uses this ID to play sound through the modem using the low-level waveout API. The WAV files must always be in 8000 Hz 16-Bit format or the waveout API will return an error. Voice modems, however, can use various PCM data formats for audio playback and recording. It is the job of the Unimodem Transform Module to transform the original audio data to whatever format the modem requires. The transform module is another Windows component.

You can tell what format a modem requires by looking in the driver's INF file for the XformID. If the driver is TAPI compliant, you should find a line similar to this:

HKR, WaveDriver, XformID ,1, 08, 00

This example is from a Conexant based modem, and the 08 indicates that this modem uses 8-bit unsigned linear PCM at 8000 Hz. For some reason, Vista has a problem with this particular format. Either it is translating the data incorrectly, or it just isn't passing the data through at all.

If you use a modem which requires almost any other sound format, the voice playback will work just fine. For example, most Intel based modems and many Agere based modems have an XformID of 04. These modems use the 4-bit IMA ADPCM 8000 Hz format. Unfortunately, Intel based modems are no longer sold.

In addition to the playback problem, if you are using Vista x64, voice applications can sometimes have a problem getting a modem wave-out ID. This problem can usually be solved by installing the following Microsoft hot-fix:

http://support.microsoft.com/kb/954912

I hope this clears some things up. Perhaps someone from Microsoft will read this and do something about it. For now, your best bet is currently an Agere based modem such as the Rosewill RNX-56AG. The Rosewill drivers are not TAPI compliant, however, so you will need to download some modified drivers from my website. This is common with Agere based modems, and the modem manufacturers need to do better when it comes to making the drivers TAPI compliant.