Noise Floor test

[Don T]

Hello:
I have been running some tests on our systems. Specifically, I am running noise floor tests. With the G5 dual 2.0, DP 4.6 and a Motu 24 I/O I am getting a 87db s/n ratio at 24bit / 96khz. Frankly, this seems pretty noisy for a 24 bit A/D. My old Fostex G16 tape machine has 86db s/n with dolby C. The noise is white unlike the traditional 16 bit triangle hash. I performed the test with a grounded input plug and recorded silence. I then put two trim plugs in at +40db each reading the level at the second plugin. It makes me wonder what other A/D boxes have as a noise floor. To say the least, I'm a little disapointed. These are line level inputs which should be giving -120db I would think.
Care to post your noise numbers so I can get an idea of what the norm should be?

[bsmart]

I'm totally in the red, overloading. This is with a dual 2 ghz G5, 2408 mk3 and DP 4.61 at 96K 24bit. There are two components, one at 80hz and one at @700hz. I compared this with a Protools HD rig. On Protools the noise was about one half that of DP and it was DC triangle waves.

[Don T]

Hello:
Can you give me some hard numbers? When you say Digidesign is half what is that in db?

Thanks

[schwarz]

To say the least, I'm a little disapointed. These are line level inputs which should be giving -120db I would think.
Care to post your noise numbers so I can get an idea of what the norm should be?

No reason to be disapointed, that's a good level. Noise is introduced by the analogue circuit before the ADC. 120dB would be impossible.

The spectrum of the noisefloor is more important than the level. If it is white it's perfect.
I have a 24i/o too, never bothered about the noise.
Did you do the test with sens set to -10dBV or 4dBu?

[Don T]

Hello:
I just repeated the test at -10db which has -84db s/n, a 3 db change. In my opinion -87db IS too noisy. My 30 year old analog console has -108db at the direct outs (2 gain stages, pre & fader). There is no need for that much noise at a single gain stage unless they are adding it to mask the digital noise inherent in the box. Why bother having 24bit (-138db s/n) if you end up tracking at 16 bit resolution? Like I said, my Fostex G16 analog tape deck has specs that good with all that cool analog tape compression too.

[Don T]

Hello:
OK, so I went home and fired up my old G3 running DP3 w/PCI 324, 2408 mk1 and a 24i. Performing the same noise test their results are:

2408 = -84db s/n (20bit)
24i = -94db s/n (24bit)

Both had white noise.

24I/O = -87db s/n

So, my 5 year old A/D has less than half of the noise than the new one.

[Don T]

Hello again:
I ran noise tests on the DA7 console yesterday and it was the best I've measured of my gear and the schools.

DA7 = -102db s/n via the mic pre's