What caused this noise?

[Jim Andrada]

I was recording our brass band again last night and when I processed the files I noticed a couple of strange things

Because I play in the band I have to do this in a set it and forget it mode so the 702 was recording continuously all evening.

I was recording M/S into an SD 702 and noticed that the first file was only around 40MB and then the piece continued in the next file, which was (as expected) close to 2GB.

So I can't figure why the file was split where it was, but also at about 5 to 7 seconds into the attached clip there are some strange noises.

I can't quite figure out what would have caused them. The only strange noises in the next 2 hours of recording were due to the musicians! No more unexpected file breaks, no problems at all. Just the first piece.

Any ideas?

http://www.j-e-andrada.com/Noise.mp3

There were some latecomers arriving and they may have bumped or jiggled the mic stand in some way, but I'm not sure if that would have caused this kind of noise.

[Chris Soucy]

That almost sounds like a power glitch. Is it possible there is a faulty mains/ supply connection somewhere? I'm assuming that there is "drop" duration which will not cause the recorder to reset but just "glitch". Maybe it actually exceeded this on one occasion which would explain the split file.

Not being familiar with the 702 I'm unsure of it's power supply configuration.


CS

[Dan Keaton]

Dear Jim,

Depending on your settings, if someone bumps or presses the "REC" button, you will either get a marker in the file, or a new file will be started.

[Jeffery Magat]

I have a 744T, and with the 702 I'm guessing you're recording straight to CF? Usually when a write error occurs, it'll start recording to a new file right after.
Did the glitch occur at the end of the 40MB file? It might be a good idea to do a media test with your recorder and look for any errors.

[Jim Andrada]

Chris,

The 702 was running off of battery so I doubt it was a mains issue.

Dan,

I noticed that someone went over to look at the unit but I think (hope) they wouldn't have pressed a button!

Jeffery,

Good point - I've recorded a few hours on this 16GB CF but don't think I ran a media test on it. It does somewhat seem like write error of some kind the more I listen to it. It's very close to the end of the file as you say so maybe write error is the most likely culprit. There were 2 or 3 glitches and a second or so later the file was split.

Edit:

I ran all the media tests in the 702 and it found no errors. That's nice, but I do worry that there are more write errors just waiting to bite me again!

I think next time I'll record to HDD simultaneously just in case.

[Dan Keaton]

Dear Jim,

I would thoroughly test the CF (Compact Flash Card).

If you have the time:

1. Power your 702 using the power supply and have a fully charged battery in place.

2. Format your CF.

3. Setup to record to your CF. Do not have anything plugged into the inputs.

4. Set the input levels to 0.

5. Press Record and let the 702 record until the CF is full.

6. Check the number of files that you have in your CF folder. There should only be one.

7. Bring the file (or files) into your Non-Linear Editor (NLE).

8. Check the files. The audio should be identical for the entire length of the recording session.

If you have a mixer, or other source of "Tone", that you could power for the duration of this test, then you could record tone instead of silence.

All Compact Flash cards are not created equal, there is a wide range of quality and design. Some types of SanDisk CF cards are known to be fake and of dubious quality.

Even with good CF cards, there is a difference in sophistication. Some do a better job of use leveling. Others have better protection against power fluctuations, they stop recording until the power is stable, preventing bad data from being written and/or data corruption.

For white papers on Compact Flash, and general information on the issues, please visit:

www.SiliconSystems.com

For information on how to spot fake CF cards, visit Ebay and read the warnings and shopping guides concerning fake memory cards

http://search.ebay.com/search/search...+CF&category0=

If you are recording important audio, using CF as your only recording medium, I would use the best CF cards I could buy.

There are at least two different major technology variations in memory cards:

Multiple Level Cell and Single Level Cell.

With MLC, multiple bits of data are recorded into one memory cell.

In the past, manufacturers recommended SLC for critical data. Currently, most manufacturers no longer make this distinction.

Personally, I would use SLC.

Another secret is that very few manufacturers will guarantee that they will not change their parts internally without notice to their customers.

Specialty, high-end manufacturers will provide this guarantee so that their devices can be used in critical applications without the user having to fully qualify (perform testing and validation) on each part their customers receive.

If they want to change the design or implementation of their parts, they create a new part number and continue manufacturing the old part number for a given number of years.

[Dan Keaton]

Originally Posted by Jim Andrada

Chris,

I ran all the media tests in the 702 and it found no errors. That's nice, but I do worry that there are more write errors just waiting to bite me again!

I think next time I'll record to HDD simultaneously just in case.

Dear Jim,

I am a little confused by your latest statements.

1. What media tests did you run?

I have searched through my 744t and I could not find a "Media Test" function.

Did you test the media on an external computer?

2. What HDD?

I thought you were using a Sound Devices 702, which only records to Compact Flash and/or an external Firewire DVD-RAM drive simultaneously, but does not have an internal hard disk drive.

Other models of Sound Devices' "7 Series" have the option of recording to a hard disk drive (HDD) and a Compact Flash and an external Firewire DVD-RAM drive simultaneously.

It may be possible to use the Firewire port on the units to record to an external Firewire HJD. I have not heard of this being possible, nor have I ever tested it.

[Brooks Harrington]

Well, never leave a recorder unattended. If you are in the band, run the cables to your chair.

[Dan Keaton]

Dear Jim,

I just set up my 744t to record to the Compact Flash only, using a slow CF card, but I recorded at 24 bits, 192k.

This, of course, is beyond the speed capabilities of the CF card (and Sound Devices specifically warns against this setup with ). I used a 256MB, 16x card, which is way too slow to record 24/192K.

I used this setup as a torture test of the Compact Flash card.

The Sound Devices detected that the CF card could not keep up. It issued a warning, and then split the files.

At the end of the recording, the 744t displayed a flashing "Slow" where it would normally show the amount of time remaining for recording on the CF card.


During playback, the sound would dropout on a regular basis. I determined that this was caused by the CF card not being able to keep up during playback.

I imported the sound files into Vegas and the audio appeared to be fine. I could not detect any missing portions, I just had three separate files to join together. Due to what I was recording, no actual input sound, I could not actually determine if anything was missing or not.


I then repeated the test, but recorded to the hard disk drive, still at 24 bits and 192k samples per second. This is a "Sound Devices Appoved" configuration. Everything recorded properly.

[Jeffery Magat]

I'm not sure if it is a speed issue although it still is a possibility.. I'm guessing it's not the issue because it kept up for two hours after the error.

Again, this could have just been a one-off write error.. anything can happen. I say you do more tests with the card, and on your future gigs hook up an external HDD for mirrored recording. Just remember that you need the power filter and external power connected to the recorder.

[Dan Keaton]

Dear Jeffery,

I agree completely, I do not suspect it was a speed issue in this case.

I just wanted to report what I learned during my torture testing of an underspeed CF card.

[Jim Andrada]

The 702 that I just got will record to exernal HDD over the firewire port. They do say to have it running from external power. I haven't tried just running from battery so am not sure if it's just a power consumtion issue or not.

There are also menu items for speed test and "test CF", all of which run fine to the same card.

They also say that it will record to all attached devices simultaneously ie to CF and whatever is plugged into the firewire port.

I like the idea of running a long test just recording silence and I'll run it tonight. I would expect the number of files to be about 8 on a 16GB card because they'll split the files at around 2 GB but any short file would be a tip off of something amiss.

[Dan Keaton]

Dear Jim,

Thank you.

I found the "Drive Speed Test", menu item 75 in firmware 2.34, which displays "Testing CF Speed" when it is operating with the Compact Flash card.

It seems intuitive that the Firewire should be able to record to an external Firewire hard disk drive.

However, I have not found any reference to recording to a HDD in Sound Devices' knowledge articles or anywhere on their website.

Sound Devices technical support is very good. I would call them up before I ran a test. In my opinion, it could not hurt, but it pays to be cautious.

[Jim Andrada]

Dan,

If you look on page 37 of the 702 manual (Firmware Rev 2.15) it talks about using Firewire HDD. as one of your options I keep two of the small 160GB units in the audio gear case all the time.

By the way I have the 702 running recording nothing to the CF - it's running along quite happily at the moment recording 24 bit/192kHz.

I think the difference between 744 and 702 re sample rate to CF might be because the 702 only records 2 channels so it should be able to run at 2X the sample rate of the 744 - I think!

Anyhow, I thought the192kHz would be more of a stress case than the 96kHz i was recording when it glitched.

Good news in all this is that what I'm recording recently is just for review by the director - our "real thing" concert will happen later. So the glitch doesn't hurt anything other than my reputation, and tuba players are always in sort of ill repute anyhow, so no big deal. I'm looking at it all as an opportunity to shake out all the problems I'm likely to run into when recording the real thing! I think I'll record the next rehearsal to both CF and HDD in parallel just to check out the system.

[Jim Andrada]

Just to summarize, I ran the 702 in record mode until all 16GB filled up. All files (except the last, which I would expect to be short) are the same size, implying no shrt files, implying no write errors (or at least no group of write errors big enough to get the 702 to terminate the file prematurely. I'm not sure if it would o this if it had a single write wrror or if it takes (for example) three erros within 5 seconds, or something like that.