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Digital Transfer between SIGNAL and DAT Recorders

Application Note 10 3

Transfer Software

Transfer software controls data flow between the DIO board and computer memory. The

digital transfer is performed under Windows, and the DIO board manufacturer normally

includes a driver which makes the DIO board look like a conventional Windows sound card.

Sound data is then transferred from the computer to the DAT by "playing" the sound file

through the DIO board to the DAT, and sound data is transferred from the DAT to the

computer by "recording" a sound file from the DAT through the DIO board. "Playing" and

"recording" through the DIO board can be handled by the Windows Sound Recorder

program, which is included with Windows. However, this program limits maximum sound

duration per physical memory, and any other program that supports record and play functions

through the Windows Sound System (such as Sound Forge, described below) should also

work. These programs normally operate on Wave files, the Windows standard. See below

for operating details.

Sound Card

A sound card can be useful to listen to the sound files received from the DAT, or check them

before transfer to the DAT. One card that is widely used is the Daytona PCI sound card

from Turtle Beach, Yonkers, NY (800-233-9377, www.tbeach.com). This is a PCI board,

which is useful on newer computers with few ISA slots, and retails for about $125. If

installing this card on a computer containing the SIGNAL analog I/O board, beware of

potential hardware conflicts. See Application Note 6, "Base Address, IRQ, and DMA

Channel Usage", for assistance. Windows can be set to play to either the sound card or DIO

board via the Windows multimedia control panel.

Sample Rate Converter

Files transferred from a DAT recorder will be received in the native sample rate of the

recorder, normally 44.1 KHz or 48 KHz. SIGNAL I/O boards provide sample rates resulting

from integer division of 4,000,000 (e.g., 43956 = 4,000,000 / 91). Therefore the SIGNAL

board cannot play DAT signals at their exact native sample rates. Note that this has no affect

on the accuracy of SIGNAL's analysis capabilities. The following table gives the nearest

available sample rate and the resulting percent error:

Native

DAT Nearest SIGNAL Percent

sample

rate sample rate error

44100 KHz 43956 -.33 %

48000 KHz 48193 +.40 %

If the percent error is significant for your application, SIGNAL 4.0 can mathematically

convert a digital signal from one sample rate to another. The process is based on

mathematical function approximation and interpolation, and can be quite accurate.

Inaccuracies introduce distortion in the resampled waveform, and resampling accuracy can be

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Engineering Design NIDisk Betriebsanweisung Seite 19