Askey Wave Device for Voice Modem Driver
A voice modem is an analog telephone data modem with a built-in capability of transmitting and receiving voice recordings over the phone line. many modems will instead send the DLE ASCII character, followed by the letter R. From then on, the modem interprets any data sent from the computer as wave audio data. Note: Some equipment listed in this article may no longer be eligible for addition on our network. If you choose to purchase your own equipment, make sure to. Askey VQC-T2 PCMCIA Voice Modem Conexant HCF 56K Data Fax Voice USB Modem .. Internal Rockwell Voice Modem Serial Wave Device.
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Askey Wave Device for Voice Modem Driver
These are industry-standard audio codecs whose implementations are well published.
It is used for both sending and receiving. For the vast majority of modems, this number will be 1 to answer a telephone call, and 0 to hang up; other numbers activate other functionality when present, such as speakerphone. Some modems answer in response to ATA - the standard data-mode answer command - but other modems will interpret this as a command to actually answer in data and not voice mode.
Askey Wave Device for Voice Modem
The audio data is always sent to the modem slightly faster than it can play it, so the modem may buffer a small portion of it and play it smoothly with no Askey Wave Device for Voice Modem or pops caused by delays in the computer's operating system. In addition, due to some extra Askey Wave Device for Voice Modem involved in doubling DLE bytes in the stream mentioned belowa small amount of extra bandwidth is mandatory to allow for this. When the modem wants the computer to temporarily pause so the playback can catch up, it temporarily lowers the CTS Clear to Send signal on the RS serial port.
The modem re-raises the signal in time for the computer to resume sending audio data before the playback buffer becomes completely empty.
Askey Computer Wave Device for Voice Modem driver - Askey Computer Modem Drivers -
Because the DLE byte can and often does occur in normal audio data, it must be sent twice to the modem when it is to be interpreted as a byte of audio data. The distinction is that the modem Askey Wave Device for Voice Modem to understand that it is to immediately abort playback now, rather than let remaining data in the playback buffer run to completion.
When the modem is done playback, it responds OK. Throttling playback[ edit ] During playback, it is necessary to send the audio data at a rate that keeps the audio playing smoothly, but without sending it faster than the modem can handle it. It is also desirable to make sure the modem can always abort playback and discard any buffered audio in case a message is to be canceled.
Message cancellation is expected by callers who already know the answers to voice prompts and provide their answer early and who would become irritated at being forced to listen to a prompt they've already responded to. There are several ways to keep Askey Wave Device for Voice Modem computer sending audio data to the modem at a rate to keep up with playback without overrunning the audio buffer. The most straightforward is to use CTS flow control.
The following caveats exist. Some voice modems have bugs in their implementation of flow control.
In particular, a large number of Conexant chipsets will sometimes drop their CTS line and never bring it back up during playback. Conexant is a hugely popular chipset in voice modems today and they otherwise implement voice commands well, making it worthwhile to consider working around this bug.
- Conexant Systems
Some Conexant chipsets will also not bring CTS back up if the "playback abort" command is sent or processed by the modem while CTS is down. Some voice modems offer a very large transmit buffer for example, 4 seconds worth of audio coupled with a bug that prevents the host from requesting an "abort playback". The result is that if a caller presses a touch-tone that's supposed to interrupt a message, and the host is providing unlimited audio data mediated by CTS alone, the end result is that the message can't be interrupted for at least 4 seconds.
A second way to throttle playback involves polling a "tick" timer provided by the host computer's operating system and based on a hardware clock that's independent of the host's CPU load. This may or may not be available, and it Askey Wave Device for Voice Modem entirely on the host operating system.
However, when available, it is extremely reliable. It is reasonable to assume that the PC needs to stay ahead of the playback by a couple of hundred bytes and that the modem will buffer this.
A third way to throttle playback involves inserting dummy DLE messages into the output stream such that the audio data takes a known amount of time to transmit through the serial port, and the playback is essentially clocked by the UART in the serial port. For example, when considering using dummy DLE stuffing, a few things must first be noted.
In a typical scenario, one second of audio might be one-byte samples, and with a small percentage of the samples being equal to the DLE byte and must be doubled, a typical second of audio might be bytes. Although it is possible that interrupt latency on the host Askey Wave Device for Voice Modem may cause slightly less than 11, bytes to be sent per second, most voice modems will buffer enough bytes before actually starting playback to permit a small skew here.
Askey Computer Wave Device for Voice Modem Modem Driver
Also the PC can be programmed to convert a second of audio into slightly fewer than 11, bytes all voice modems will buffer a small overrun without the need for flow control as long as it Askey Wave Device for Voice Modem no more than a few hundred bytes. It makes sense only with external serial modems that are physically clocked to a specific bit rate by a clock generator behind the external serial port.
The modem never stops transmitting until the computer tells it to stop, which is usually with CTRL-C. Before, during, and after recording, the modem may notify the computer host of specific events including, but not limited to, the following: