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Topic: Background noise- causes/strategies to deal with it? (Read 6039 times) previous topic - next topic
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Background noise- causes/strategies to deal with it?

Hey folks,

Final question for today (well, maybe one more). I'm really trying to revamp the way I do things!

I've been running a M-Audio FireWire Audiophile to record WAV files, and I use Cool Edit Pro 2.1 to edit WAV files. A friend recently told me you could monitor the recording level with CEP, which I promptly tried out (turned out all I had to do was right-click the VU level and select the monitor button!).

My FW Audiophile registered, with no sound equipment on, about 72 dB. With my sound equipment on that went to 60 dB.

My friend was having a similar problem- his Turtle Beach Riviera card was registering as 60 dB with similar equipment as well.

Given both the sound cards are better and supposedly far less noisy than that, what could be some causes of the noise registering that high, and what can be done about it?

Regards,
- Spike

Background noise- causes/strategies to deal with it?

Reply #1 –
Ground loop would be a good start.
Acid8000 aka. PhilDEE

Background noise- causes/strategies to deal with it?

Reply #2 –
Hey Acid,

You're from Sydney eh? Cool! I'm from Adelaide.

I've used a ground loop isolator (I presume that's what you mean) with my sound modules and Audiophile before, but they change/distort the sound with some frequencies. But, that was with the laptop I think, maybe it would be different with this desktop (a pretty good machine). (Though that doesn't sound logical to me.)

Maybe I used one of these:
Quote
Automotive "Signal Isolators". This method is a "last resort" means of isolating line-level interconnections. One source for these devices is your local Radio Shack (#270-054, $14.99). WARNING: because it uses transformers for coupling, there is the possibility of signal degradation, loss of frequency range, and increase of signal distortion. If you decide to go this route, consider installing one on every device feeding your main preamp/receiver. NOTE: these units are not suitable for coupling RCA composite video feeds from video equipment!
(Source: Ken Simmons)

In fact, here's what I used:
http://www.crutchfield.com/S-rZTwJP0zRBY/c...0&I=127SNI1

Is this one of those "Automotive" ones? Maybe I wasn't thinking when I bought this (I tried this a while back).

- Spike

Background noise- causes/strategies to deal with it?

Reply #3 –
I got rid of a ground loop problem without buying an isolator. I simply disconnected the outer shield of the cable from the connector on one end. As a result I had a significant reduction in noise between my Audigy 4 and low end 70s amp (Pioneer SA-5300).

Heh good to see another Aussie member btw.

Edit: You might find this useful. Sorry about the poor terminology as I'm not the most experienced with audio equipment.
http://www.hydrogenaudio.org/forums/index....st&p=426327
Acid8000 aka. PhilDEE

Background noise- causes/strategies to deal with it?

Reply #4 –
CoolEdit has useful tools to identify problems. What does a Frequency Analysis graph show you about a noise floor recording? If you don't have high 50 or 60Hz peaks (depending upon your mains frequency) and possibly some higher frequency harmonics of same, then looking for grounding problems is a wasted effort.

If this -72dB level with nothing plugged into the soundcard? Are you measuring from a line level input? If yes to both of those, there is some serious problem with either the device or the computer. No ground loops should be involved in that simplified measurement. What is the Average RMS level of a noise floor recording? What is the "sound equipment" that adds 12dB of noise?

Regarding you other thread about the input level being too high, I see in the M-Audio specs
user-assignable front-panel level control (output, input, software return, aux send)
The box includes a mixer of sorts, and that statement seems to say there is a level control (which is normal for a mixer). Perhaps you just are not using it correctly?

Background noise- causes/strategies to deal with it?

Reply #5 –
72dB relative to what?  Full scale volume at 0dB?  That sounds really strange.  Can you double check those numbers with RMAA?

Background noise- causes/strategies to deal with it?

Reply #6 –
Quote
CoolEdit has useful tools to identify problems. What does a Frequency Analysis graph show you about a noise floor recording? If you don't have high 50 or 60Hz peaks (depending upon your mains frequency) and possibly some higher frequency harmonics of same, then looking for grounding problems is a wasted effort.

I didn't really see much. What do you mean by a noise floor recording- recording silence for 15 seconds and then playing it back, watching the frequency graph move?

Quote
If this -72dB level with nothing plugged into the soundcard? Are you measuring from a line level input? If yes to both of those, there is some serious problem with either the device or the computer. No ground loops should be involved in that simplified measurement. What is the Average RMS level of a noise floor recording? What is the "sound equipment" that adds 12dB of noise?

-72dB is with the M-Audio turned on (powered by its' adapter, not just bus power) and nothing connected to it.

Actually, it varies constantly, and really is around 68dB or something.

And as you pointed out in another thread, no, not line level inputs. I have the device powered on and the FireWire port connected to my PC (which is through a PCI sound card with FireWire ports, which could be a problem, I guess).

The sound equipment I refer to is 4 old sound modules, which ones shouldn't matter, though I'll write if you need to know.


Quote
Regarding you other thread about the input level being too high, I see in the M-Audio specs
user-assignable front-panel level control (output, input, software return, aux send)
The box includes a mixer of sorts, and that statement seems to say there is a level control (which is normal for a mixer). Perhaps you just are not using it correctly?

Like I said, although there's the mixer part of the control panel, changing the sliders doesn't seem to have any bearing on what volume level is recorded, although in my headphones, the volume changes.

And, maybe I'm not using it correctly. I presumed it'd be the same as any other sound card I've used. I posted these topics to make sure I'm doing things correctly, as the game music website I run isn't going to be much cop if I can't use my equipment correctly. That's why I appreciate your comments 


Quote
72dB relative to what? Full scale volume at 0dB? That sounds really strange. Can you double check those numbers with RMAA?

Yeah, I should RMAA my FW Audiophile. I'll check it out later.



EDIT: Check this *old* thread out. http://www.hydrogenaudio.org/forums/index....showtopic=12349

What do you guys think, is my problem the same as the Audiophile problem described (even though the devices aren't the same)?


Additionally, when I have my sound modules plugged in to my M-Audio Audiophile through line in, as per that thread should I run them on higher voltages and amperage than the M-Audio card? (Someone says it lowers distortion and improves SNR quality, unless I read it wrong- that thread is very confusing to say the least.)

I mean, that'd be pretty easy to do, to replace my adaptors, which are just barely above their specs (e.g. one module needs 9V, 500 mA, and it's using a 9V, 500 mA AC adaptor. The FW Audiophile uses 12V, 1000mA DC. Using the logic from the thread, should I use all 12V 1000mA adaptors with my gear?  )
And would that be a problem in itself- running a bunch of AC synth modules through a DC soundcard?

Damn, I hate sounding like a newbie. But I have a reasonable understanding, and prefer being honest so you guys can deal easier with me. Just forgive some stupid questions.

Regards,
- Spike

Background noise- causes/strategies to deal with it?

Reply #7 –
Do you really have "a PCI sound card with FireWire ports"? A PCI card to provide firewire ports is common enough, but I don't recall any PCI soundcard with firewire ports. There is hardly enough room on a PCI soundcard for the necessary audio components.

The only analogue inputs your card has are line-level. The firewire connection is just the way the digitized data is sent to the computer.

I looked at M-Audio site. The level control on the box is only to control the monitoring levels. There is no mixer except the DSP for directing and combining outputs. Thus, the input level  cannot be adjusted. The device is quite normal in this respect.

The Firewire Audiophile's published specs are very near those of the Audiophile 2496. Its noise floor results should therefore be about the same. Perhaps the converters in the box are the same ones used on the PCI card.

A system noise floor recording , capturing just the contributions of computer and soundcard,  is done by recording from the analogue inputs with nothing connected to the input jacks. Recording at 32 bit, 44.1kHz is a good choice. Record for 12 to 15 seconds. Select a few seconds of that recording to measure, say seconds 7 through 10.

Ideally the levels will be the same across the entire recording, but it is not unusual, while the clock is settling down in the first second or so,  for the levels to vary rapidly. You can easily find out by clicking on the vertical zoom-in until the wave form is clearly visible on screen. Anyway, I always avoid getting too close to the endpoint  when taking measurements.

Analyze/Statistics gives some useful numbers. If you were measuring a nice clean sine wave, you would see Peak Amplitude and RMS Average just about equal, computed relative to a sine wave, or Peak about 3dB higher than RMS, computed relative to a square wave. A noise floor recording, not being a nice sine wave, should have a much larger difference between Peak and RMS values; the RMS values are usually more indicative of what you will hear (or not hear). My PCI soundcard noise floor is about  -86dB peak, -98dB RMS, relative to a 0dBfs square wave. Your soundcard should be about the same. If noise level are much higher, something is wrong.

With that same three seconds of the recording selected, run Analyze/Frequency Analysis. Click on Scan to build the graph. I like to use FFT Size 16384 on just about everything; it gives enough detail for most of my purposes. Always running the same analysis makes comparisons between different samples more meaningful.

If you have any hum problems they will show up as significant peaks on a curve that otherwise is unlikely to have any major variations. Its not unusual for little boxes like the FW Audiophile, using a wall wart supply, to show some 60 (or 50) Hz, along with the first few harmonics of same. These really stand out on the Frequency Analysis graph, but they probably do not represent enough energy to be heard, or to make any significant difference in your recordings.

If you see large hum peaks, and the Statistics figures are much higher than I indicated they should be, you can use Transform/Filters/Notch Filter to remove the hum. Leave the Frequency Analysis window open while you adjust the Attenuation and Notch Width to eliminate those peaks.

Run the Notch Filter, scan your selection to see the results, click on Undo to try again. When the hum peaks are flattened, run Analyze Statistics again to see how much you have to gain by eliminating the hum at its source. If all you have is the average dribble from the wall wart supply, the numbers, pre and post filtering, will not change much.

You can then proceed to making noise floor recordings of your audio source equipment by plugging its outputs into the soundcard inputs. Record while the sound equipment is running at idle. This will measure how much noise they add to the basic system. If you have ground loop problems, those should show up as greatly increased peaks on the Frequency Analysis graph of the new recording.

If your synth modules are designed for 9V, 12V might destroy them. If it actually worked well, it would give them the potential for higher output levels. Since their output levels are already too high for the soundcard's inputs, it doesn't seem too profitable.

You don't have "DC soundcard vs AC synths." Almost everything electronic runs on DC. Anything supplied by the mains (rather than by batteries) starts with AC, but that must be converted to DC before powering the circuits. Sometimes wall warts put out AC; the rest of the power supply resides inside the device chassis. Sometimes the major parts of the power supply are inside the wall wart unit; it sends already rectified power to the device.

Background noise- causes/strategies to deal with it?

Reply #8 –
Thanks a bunch man, you're really invaluable. I really appreciate this. I'll try it tomorrow.

- Spike

Background noise- causes/strategies to deal with it?

Reply #9 –
Quote from: Spikey on
I've been running a M-Audio FireWire Audiophile to record WAV files, and I use Cool Edit Pro 2.1 to edit WAV files...

What are you doing? What are you connecting to the sound card?
 

Background noise- causes/strategies to deal with it?

Reply #10 –
I connect 4 vintage synths (well, sort of vintage- Roland's MT-32, SC-55mkII and SC-8850, and Yamaha's MU100R) through analog RCA daisychaining.

I'm going to get a mixer soon, though.

Reply to Andy coming later.

- Spike