Problems joining split recordings

[cubdukat]

I had this problem with DC8, but now I'm having this in DCart10 as well.

Occasionally an album I record will exceed the 2GB file limit and be split into two parts, usually because I don't catch the end of the first side in time. Once I edit out the lead-out portion, I am able to append the second file, but when I save the combined file, the joined second half becomes nothing but white noise.

This only happens at the file's native resolution of 24/96. If I downconvert both halves to 24/48 and then join them, the corruption doesn't happen.

Is there any way to work around this problem without me having to downconvert first? The only thing I end up doing before downconversion is normalization. Does it matter whether I do that in 24/96 or 24/48?

[cubdukat]

The left example is after appending the two files, but before saving. The right example is after saving and normalizing. The save did not produce the corruption this time like it normally does, but the normalization did.

[Craig Maier]

It is probably a bug. But, it may help to realize that an LP (album) only has around 50 dB of signal to noise ratio. So, the use of 16 bits is way more than adequate providing over 90 dB of dynamic range. 24 bits is way, way beyond the humans capability of discerning that degree of dynamic range (24 bits is about 140 dB of dynamic range). So, what you are doing is trying to record something with 50 dB of signal to noise ratio with a system capable of (theoretically) 140 dB. So, I would recommend using 16 bits and 96 kHz sample rate.

Craig

[cubdukat]

Interesting. I'll have to try 16/96. I always though that bit depth and sample rate were of equal importance.

[Craig Maier]

Sample rate is more important than bit depth. The software takes advantage of ultrasonic signals that are digitized when using a higher sample rate when discriminating impulse noise from music. But, bit depth beyond 16 bits is simply not of any value audibly. It's easy enough for you to try it for yourself. Record both ways (16 bits vs 24 bits). We will give you a free copy of the 1500 dollar forensics audio if you can prove that you hear a difference (use double blind techniques).

Craig

[cubdukat]

I'll take your word for it. I have a 10% hearing deficit in one ear anyway

I'm trying it out with a very good first-generation pressing of Michael Jackson's "Bad."

[Craig Maier]

16 bits will sound perfect. After all, that is what a Red Book CD uses (16 bit linear pcm). And today, hardly anyone even listens to CD quality sound - - - is mostly compressed .mp3.

Craig

[cubdukat]

I think I might have hit upon the solution. I ran the DC Offset filter first and joined the two files. When I saved it, it didn't give me the white noise problem. So now I have added DC Offset filtering to my workflow whenever I have a file that goes past the 2GB limit.

[Craig Maier]

Ok - that is good to know. I was not aware that modern A/D converters produced DC Offset (I know that the earlier ones did, however).

Thanks for sharing your discovery. As an aside, do you know what brand your sound card or chip set is?

Craig

[cubdukat]

The internal one is a Realtek S1220A for motherboard sound, but I wasn't happy with it so I reinstalled an older SoundBlaster X-Fi Titanium PCIe card. I still haven't gotten the external USB interface yet, but I intend to.

[Craig Maier]

Was it the Sound Blaster that had the DC offset?

Craig

[cubdukat]

As it turns out, it's something else in my system. Even when the tonearm's at rest, the VU meters are showing at least 10dB of something constantly going, even when it's completely silent. There's something going on in the system. I'm debating whether I should break the recording process away from the compluter and into a standalone digital recorder, and then just walk the SD card over to the computer to work in DCart10, or see if the external audio interface I was going to get might solve the problem.

[Craig Maier]

That is hard to say from where I sit. Most commonly the residual noise coming from a turntable recording system arises out of ground loops. Bonding the turntable ground strap to the preamp and also to the computer usually helps with this problem. Also, all of the devices associated with the recording process need to be plugged into the same grounded outlet strip. That is just good practice, but the noise could be caused by other mechanisms too. If the turntable is too close to another electrical device, that can cause unwanted noise coupling into the phono cartridge.

Craig

[Craig Maier]

I use a 6 foot length of 18 AWG lamp cord (both sides twisted together at each end) connecting the turntable chassis to the preamplifier chassis. I also use a second 18 AWG lamp cord (again, both ends twisted together to get the lowest possible resistance) connected between the preamp chassis and the computer chassis. I use one of the screws on the back of the computer to secure this wire to the computers chassis ground. I also keep my turntable away from the computer by about 5 feet to minimize magnetic field coupling of the computer circuitry from impinging upon my magnetic phono cartridge. This combination of things give me a very clean audio transfer of my records onto my computer hard drive.

Craig