Topic: TASCAM DR-680 portable 8-track #6

[lukpac]

Interesting. I don't have my 680 anymore, but seem to recall that the "High" gain setting was considerably noisier throughout the entire gain range and would run on "Low" with the gain cranked up. Maybe I'm just not remembering things correctly.

On mine it is *significantly* noisier on "Low" with the trim cranked up. I can make some clips if anyone is interested.

[Carlos E. Martinez]

Your findings should be right on. If you use Low gain and crank the level pot up, all the chip noise will be amplified by the following chains.

[Chuck]

Interesting. I don't have my 680 anymore, but seem to recall that the "High" gain setting was considerably noisier throughout the entire gain range and would run on "Low" with the gain cranked up. Maybe I'm just not remembering things correctly.

On mine it is *significantly* noisier on "Low" with the trim cranked up. I can make some clips if anyone is interested.

This seems to go against how most recordists use the DR-680.

I use the low gain (MIC IN) for recording live music with condenser microphones.

[lukpac]

This seems to go against how most recordists use the DR-680.

I use the low gain (MIC IN) for recording live music with condenser microphones.

Above a certain input level (between source volume and microphone sensitivity) it would obviously make sense to use Low gain, but for lower levels High gain is definitely a necessity unless you want a noisy recording. Fortunately I only made that mistake once.

[achalsey]

I have considerable noise on high gain mic in.  Ruined two separate recordings a couple months ago.  Tested it at home through the headphone out and there was a lot of hiss.  This is obviously not scientific, but personally will avoid using high gain if at all possible in the future.

[lukpac]

I have considerable noise on high gain mic in.  Ruined two separate recordings a couple months ago.  Tested it at home through the headphone out and there was a lot of hiss.  This is obviously not scientific, but personally will avoid using high gain if at all possible in the future.

What do you mean by "a lot of hiss"?

When monitoring/recording, if you have the input switch set to "Low", and then switch it to "High", you'll definitely hear more noise, but that's only because the signal is now significantly louder. If you level match via the Trim function, that should not be the case.

For example, if you have 2 identical mics plugged into channels 1 & 2, with channel 1 set to "Low" and channel 2 set to "High", and the Trim is set to 0 for both channels, channel 2 will be noisier than channel 1, but it will also be significantly louder. If you then adjust the Trim on channel 1 to +23 so the input signal is at the same level on both channels, there should now be more noise on channel 1.

Make sense?

[Gutbucket]

General best practice-
Adjust the gains in order: first the high/low switch gross adjustment (first stage), then the trim fine adjustment (second stage).  In setting the first stage high/low switch, choose the position which allows a trim setting closer to its +/- zero position.  If you find you need to adjust trim towards the extremities of its range and switching the first stage input switch the otherway allow you to keep the trims closer to zero, do that.

[lukpac]

General best practice-
Adjust the gains in order: first the high/low switch gross adjustment (first stage), then the trim fine adjustment (second stage).  In setting the first stage high/low switch, choose the position which allows a trim setting closer to its +/- zero position.  If you find you need to adjust trim towards the extremities of its range and switching the first stage input switch the otherway allow you to keep the trims closer to zero, do that.

Yeah, I think the only question (one which I haven't really investigated yet) is what the best "switchover" point is. That is to say, I know that High/0 sounds better than Low/+23, but what about High/-10 and Low/+13, or High/-20 and Low/+3?

Is anybody interested in an example file?

[Gutbucket]

High with a heavy dose of negative trim may well have a lower noise-floor but also reduces headroom though the first gain stage.  If the first stage clips then that's usually more objectable than a bit more noise down at the quiet end, partly because if the source is loud enough to clip the input stage, you'd need to use pretty heavy amounts of dynamic compression to bring the noise-floor up into the range of audibility at normal listening levels.

In regards to using the line on the meters as a good level setting target, I find that to be a pretty good safe zone for most things and just shoot for that.  I did once see momentary peak clipping of the input stage with the meters otherwise riding the 'line', but that was with on stage mics in close proximity to a drum kit with large transients and a relatively low average level (wasn't close mic'ing the kit but only ~2-3 feet away, the mic pointed at the snare).  The clipping indicator lit momnetarily although the meter read on or just over the line.

[achalsey]

I would be interested.  I definitely understand what you're saying between high/low difference at the same trim level though.

Here is a track of one of the ruined sets.  I just amplified it starting at 40 seconds. 

This was AKG CK 63 > Naiant coupling/PFA > (adapters) > 680 mic in, gain on high, trim pretty high, I want to say like over 20.  I will say however, that I was running to channels 5/6, 1/4" in with XLR > TS 1/4" adapters.  Not sure if that affected it.  Someone mentioned the unbalanced signal might have been the culprit?

https://soundcloud.com/achalsey/680-self-noise

[lukpac]

I would be interested.  I definitely understand what you're saying between high/low difference at the same trim level though.

Here is a track of one of the ruined sets.  I just amplified it starting at 40 seconds. 

This was AKG CK 63 > Naiant coupling/PFA > (adapters) > 680 mic in, gain on high, trim pretty high, I want to say like over 20.  I will say however, that I was running to channels 5/6, 1/4" in with XLR > TS 1/4" adapters.  Not sure if that affected it.  Someone mentioned the unbalanced signal might have been the culprit?

https://soundcloud.com/dynamically/680-self-noise

FWIW, I get an error when I click that link.

If you had the gain set to High and the trim at +20, I doubt the gain had anything to do with it. That is, if you still weren't clipping with the trim set to +20, there should have been *plenty* of headroom for the High input.

Now, if you had the trim set very *low*, like -20, I could see the possibility of the input stage overloading.

I'll try and remember to create a sample clip tonight.

[achalsey]

fixed.  Also, I wasn't under the assumption of anything overloading.  I was just talking about self noise from the machine.  It seems very noisy to me with the gain turned up too high.

[Gutbucket]

I will say however, that I was running to channels 5/6, 1/4" in with XLR > TS 1/4" adapters.  Not sure if that affected it.  Someone mentioned the unbalanced signal might have been the culprit?

Haven't listend to the sample, but that's likely to be your issue.  Besides being unbalanced and more sensitive to interference noise, with one leg of the balanced signal shorted to ground the signal level is reduced by about 6dB which effectively increases the noise floor by that amount (I'm pretty sure).  Switch to a TRS instead of a TS plug, the cable remains balanced and you maximise signal to noise.

[lukpac]

fixed.

Thanks.

By "ruined", do you just mean it's noisy? Because while I hear plenty of noise, I don't hear any overload or distortion.

If you had recorded on Low and bumped up the level in post to match, it would have been at least that noisy, if not more so. It seems that the problem was very low input levels from your mics, not anything with the High gain setting on the 680.

This was AKG CK 63 > Naiant coupling/PFA > (adapters) > 680 mic in, gain on high, trim pretty high, I want to say like over 20.  I will say however, that I was running to channels 5/6, 1/4" in with XLR > TS 1/4" adapters.  Not sure if that affected it.  Someone mentioned the unbalanced signal might have been the culprit?

I don't understand this. How could you have been using phantom power adapters with a 1/4" TS adapter? The TS plug would have shorted out the +48V between the sleeve and ring.

As far as my clip goes, I remembered that I had already recorded one:

https://dl.dropboxusercontent.com/s/qdjam3wyepnup4e/SM57_st.flac

SM 57 -> ART SplitCom Pro -> DR-680 ->
channel 1: Low gain, Trim set to +23 (mixed left)
channel 2: High gain, Trim set to 0 (mixed right)

Note that the signal level is equal on both tracks, but there's significantly more hiss on channel 1.

[achalsey]

This was AKG CK 63 > Naiant coupling/PFA > (adapters) > 680 mic in, gain on high, trim pretty high, I want to say like over 20.  I will say however, that I was running to channels 5/6, 1/4" in with XLR > TS 1/4" adapters.  Not sure if that affected it.  Someone mentioned the unbalanced signal might have been the culprit?

I don't understand this. How could you have been using phantom power adapters with a 1/4" TS adapter? The TS plug would have shorted out the +48V between the sleeve and ring.

That....is a good point.  I had not considered that.  Not sure how it worked, but could obviously be the issue.