Hello Flexers, I am in route back from Dayton where was so good to see many of you our customers and to have many more join in the fun.
I do want to add a couple of points that have been missed here. Virtually all professional audio cards use +4 dBu as the nominal input level. 0 dBu is 1 mW into 600 Ohms. As I recall, the peak level before overload on most cards will be 10-20 dB above that. Most of these pro audio sound cards actually use some attenuation on the front end to prevent overload and give headroom at the nominal level. Attenuation introduces noise. On the other hand, the attenuation can be used to our advantage because the SDR-1000 utilizes a very high dynamic range preamp ahead of the detector. The total system gain ahead of the sound card is about 40 dB. This allows us to have the high dynamic range while not overloading the sound card. Most 16 bit cards use -10 dBV nominal inputs, which will overload at much lower levels. The only number I pay much attention to on the sound card specs is the dynamic range as measured in 20 KHz. Note that you typically need to subtract 3dB from the A weighted spec to get a more accurate picture of how it will work in our application. The Delta 44 is rated at 99 dB A Weighted and the Firebox at 107 dB A Weighted. The maximum theoretical specification for a 16 bit card is 96 dB + 1.72 dB (going from memory so I could be wrong on the 1.72). Note that the Turtle Beach Santa Cruz was one of the best 16-bit consumer cards when it was available. One of the reasons for this was that they actually used an 18-bit converter but only presented 16-bits to the bus. Even with that, it did not quite reach 16-bits of real dynamic range. It also would overload at much lower levels. So the Firebox will be 10 dB better than a PERFECT 16 bit converter, which does not exist on the consumer market to my knowledge. Don't forget that 10 dB is a factor of 10. I will take a factor of 10 improvement any day. Heck 3dB is twice as good in my book. The AKM chip converter mentioned earlier is rated by the manufacturer with an A weighted dynamic range of 123 dB so drop 3 dB off of that an you are just a fraction over 20 bits (ENOB) with one of the best converters. 120 dB down from 5V is 5uV! Very good board and circuit design is required to achieve that dynamic range. This is about what the $1000 cards do (e.g. Lynx 22). By the way, they work great with the SDR-1000. ;>) 73, Gerald Gerald Youngblood, K5SDR FlexRadio Systems Ph: 512-535-5266 Fax: 512-233-5143 Email: [EMAIL PROTECTED] Web: www.flex-radio.com _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
