Thanks for the explanation and references. They will be quite helpful. Bob Russell L. Harris wrote:
* Bob McGowan <bob_mcgowan@symantec.com> [070226 11:14]:Russell L. Harris wrote:Within the past year or two there have become available a number of alternatives to the computer sound card. These eliminate the pitfalls (especially the electrical noise) associated with sound cards, as well as the problem of hardware and software obsolescence. Some are stand-alone flash memory recorders with broadcast-quality microphone inputs (i.e., balanced XLR). These typically have a usb interface which can be used, after recording, to transfer the digitized audio to the computer for editing or processing; or you can make the transfer using a flash card reader. Also now available are a number of recording interfaces with broadcast-quality microphone inputs; these also typically interface to the computer via usb or firewire. Some claim to require no proprietary software for recording.Could you provide some additional information or pointers to it, regarding your comments about sound card electrical noise, and perhaps some references to the hardware you mentioned?Hi, Bob.From the standpoint of electrical noise, the interior of a computer isextremely "dirty", because of the nature of digital signals (sharptransitions, which correspond to high-frequency components).In the case of a microphone input, an analogue audio signal in the millivolt or even microvolt range must be amplified by a factor of a thousand or more before it is digitized. Careful shielding and grounding, together with the use of balanced circuitry, are essential to prevent the analogue signal from being corrupted; the measures require good engineering and typically are expensive. Once in the digital realm, there is no major problem with integrity of the signal. Recording analogue sound with a sound card plugged into a PC is analogous to recording birds singing in the backyard while the kid next door and his rock band are practicing in the garage. Putting the low-level amplification and the digitizing circuitry in a box external to the PC chassis is much like doing your recording in a sound isolation booth. One of the best sources of information regarding the problems of electrical noise and methods for handling the problem is the literature of manufacturers of sound cards and audio interfaces. Go to the web page of a broadcast-gear supplier such as www.bswusa.com and view the on-line catalogue, or request a catalogue to be mailed to you. The catalogue lists a variety of broadcast-grade sound cards and external audio interfaces. Then go the web pages of the various manufacturers. Again, if you are serious about signal integrity, the use of balanced circuitry is essential. Balanced lines consist of a twisted pair of conductors with a shield, and typically use the Canon XLR connector or a 1/4-inch TRS (tip, ring, sleeve) phone plug. Apart from its use in digital applications, coax cable (in which the "shield" is an integral part of the signal path) is used only on non-critical consumer gear. RLH
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