rgc@wam.umd.edu (Ross Garrett Cutler) (10/25/90)
Hello, Sorry for the long delay, but not much response was generated by these two questions. Anyway, I've played around with MonsterScope, and it's quite nice for audio-range frequencies. This suits my needs for now. Too bad the source doesn't come with the NeXT. As for real-time acquisition, the NeXT is not sufficient. I was hoping to hook up an A/D converter to the DSP port and read in my data that way. But there's no guarantee that when something else slows down the system I won't lose any data. You could argue that just don't let anyone else on the system while you're acuiring data; but what if someone mails me some voice mail; or what if Mach just hicups as UNIX systems do sometimes. You could also say that you've used Digital Ears and have had no problems. But have you tested it? The rate of data I need to sample is not much, but if I lose a millisecond anywhere, it's no good. I've talked to the makers of Digital Ears and they admit that you could lose data and there's *no* indication if you do. Oh well, too bad. I'm still getting a NeXTstation for home, but it would be nice if we could replace the PC's in our labs with them as well. -- Please email -- I'll summarize. Ross Cutler University of Maryland, College Park Internet: rgc@wam.umd.edu
cpenrose@sdcc13.ucsd.edu (Christopher Penrose) (10/26/90)
In article <1990Oct24.210232.24492@wam.umd.edu> rgc@wam.umd.edu (Ross Garrett Cutler) writes: >But have you tested it? The rate of data I need to sample is not much, >but if I lose a millisecond anywhere, it's no good. I've talked to the >makers of Digital Ears and they admit that you could lose data and there's >*no* indication if you do. If you are sampling audio data, there are two major indicators of data continuity. Your ears, and the data itself. Discontinuties are extremely noticeable: radical and isolated signal changes are heard as broadband clicks. If your hear a click and or a drop-out, chances are that your data is incomplete. You can graph the data and pin-point discontinuties. By the way, I have managed to sample 44.1Khz stereo direct to disk on my NeXT while running other cpu-intensive jobs in the background without any data loss. I was impressed. I also have the old 68030: a NeXTStation with a 68040 will probably convert/and or sample audio with great ease. Receiving mail is probably not going to cause sample data loss. Christopher Penrose jesus!penrose cpenrose@ucsd.edu
Eric.Thayer@cs.cmu.edu (Eric H. Thayer) (10/27/90)
In article <1990Oct24.210232.24492@wam.umd.edu> rgc@wam.umd.edu (Ross Garrett Cutler) writes: > The rate of data I need to sample is not much, > but if I lose a millisecond anywhere, it's no good. I've talked to the > makers of Digital Ears and they admit that you could lose data and there's > *no* indication if you do. I'm sorry I don't have anything non-annecdotal concerning data loss on the NeXT. But, it should be straightforward to design a system which would dectect lost data. The DSP subsystem itself on the NeXT is not subject to the scheduling whims of the kernel. You can design your DSP code such that with every DMA transfer it would send the size of the data received so far on the DSP SERIAL PORT ITSELF. This number will be accurate (modulo 2^23). So on the 68k side, you could check to see that the tally of the amount of data you have received agrees with the DSP's tally. If they don't agree, then somewhere some data was dropped. If they do agree, you can be confident that you have received the same amount of data. If you were still concerned about integrity of the data, you could gain more confidence by keeping a running checksum going on either side too. What I haven't said that is still important is that on the DSP side you should also check for overrun errors on the DSP serial port. The sounddriver has a reasonable setup for data aquisition. You need to ensure that you always keep at least one region waiting to be recorded, but if your code can meet that requirement everything SHOULD be ok. Our data aquisition code so far has been able maintain this requirement. So far, we haven't experience problems that were attributed to data loss. But your message has gotten me thinking about putting the above tallying feature into our data collection system just to make sure. ---------------------------------- Replies can have NeXT attachments in them Phone: (412)268-7679