Topic: Why is my recording hissy?

[depp91]

Hello folks!
I have a question about a specific recording anomaly I encountered when I recorded a concert a week ago. I used my newly repaired SP-CMC-4Us (low sensitivity mod), a 12V battery box and my Sony PCM-A10 and recorded in 24bit mode. The concert was a solo show with an electric guitar but I expected loud levels, so I chose the audio-in setting and started at level 14 but increased levels up to 22 in the end because the concert was not as loud as expected. At 22, I arrived at the sweet spot where the recording is loud enough and still has enough headroom to prevent clipping. All went perfectly during the concert, but as I listened to the recording, it turned out to be very hissy! Even after the first songs, when I had already adjusted my levels to 22, there is audible hiss!
I've now tried to replicate the problem at home, directing the microphones at my speakers at home. Using the audio-in setting again and trying out levels from 22 to 30, the hiss is again very audible.
Using the mic-in setting, the hiss is not there.
What's the conclusion?

Again, my equipment and settings for the concert recording were:
Mics: SP-CMC-4U (AT U853s, low sensitivity mod)
Battery box: SP-SPSB-20
Recorder: Sony PCM-A10 (24bit/48khz; Audio-in setting, manual gain - started at 14, increased to 22)

[nassau73]

I don't have an A10 but I looked up info about the recorder.

As I suspected - Audio In is for an external device.

[aaronji]

Using the mic-in setting, the hiss is not there.
What's the conclusion?

Use the mic input...

Those mics are pretty low sensitivity, so if the source was not that loud, you would need to add a lot of gain if you use the audio in. That could result in hiss.

[aaronji]

^ To expand on that a little, I think that there are basically three factors that affect the mic or line/audio input choice: 1. sound pressure levels, 2. microphone sensitivity, and 3. input sensitivity. At a given SPL, mics with a given sensitivity will output a signal at a given voltage (see Table 1 on this page). The recorder's inputs (mic/line) can only accept a certain maximum input voltage, so the choice comes down to whether you overload or underwhelm the input you choose. With a decent recorder, and mics that aren't on the extremes of sensitivity (in either direction), the mic input should generally be OK if you aren't adding any gain via a pre-amp. With a pre, or a combination of dBSPL/mic sensitivity/input sensitivity that would overload the mic input, line-in is the way to go. My two cents and all, of course.

Unfortunately, it is kind of hard to estimate what the sound pressure levels will be (absent previous experiences with the band, venue, and soundman). If you search it, you will see a range of dbSPL estimates for a rock concert. Those go up to 120 dB, but I think that might be an occasional peak, as sustained levels that high would be excruciating after a short time. The good mic and recorder manufacturers (hopefully) specify the sensitivities of their products, though, so you can ballpark the whole thing decently well...   

[EDIT:] As some food for thought, the original nBox had a fixed 20 dB gain (if I recall correctly). The mics frequently used with that pre, the Schoeps MK4s, have a sensitivity of 15 mV/Pa. That combination, used with the line input on a wide range of recorders, has produced a ton of great tapes.

[Gutbucket]

Aaron posted before I hit reply on essentially the same message..

Because you're using a battery box to power the mics, you should be able to use either Mic in or Audio in (line in).  A battery box replaces the need for plug-in-power being supplied by the recorder, but won't cause a problem if that is still being supplied by the recorder.  If you weren't using a battery box you might need to choose Mic in to activate PIP on the A10 and power the mics.  Not an A10 user myself and not sure about that.

The other thing that choosing between Mic in or Audio in may affect is input sensitivity, which is what you should take a look at if you are experiencing noise problems.  Not sure but looks like in addition to the choice between Mic in or Music in, there is a separate menu for sensitivity adjustment.

The low sensitivity mod on the mics increases their high SPL handling ability at the cost of reduced suitability for low SPL material.  With the higher SPL handling capability comes higher microphone self-noise at the quiet end of the scale, which equates to more hiss when a low level recording is amplified. Similarly, choosing lower input sensitivity on the recorder accommodates higher SPLs without clipping.. at the cost of increased noise when amplifying the quiet sections. 

So, try a higher input sensitivity setting on the A10 which provides a comfortable range of input gain adjustment able to get the peaks to where you want them on the meters when recording in that particular situation.  If more than one sensitivity setting allows for getting levels where you want them (not clipping, but also not too low), try both, then use whichever results in a cleaner recording.

[seethreepo]

Low battery in the battery box is also a potential villain in this scenario.

[nulldogmas]

I use this exact signal chain as my main recording setup — low-sens AT-853s > 12v battery box > A10 set to line in — and have not had problems with hiss. And a level of 22 for solo electric seems pretty reasonable from my experience, so I doubt a bad battery is to blame.

In short: I dunno, man, that's weird.

[vibrioidxire]

I've been having this problem too with my A10! I'm assuming the A10 has a bad S/N ratio (or at least mine does). I tested my SP-CMC-4U > SP-SPSB-10 setup into my D10 and there's zero hiss.

[depp91]

Thanks a lot for all the excellent and thoughtful answers!
I guess I'll try the mic-in setting at my next concert (if it's not too loud, at least) and hope I'll be able to lower the levels enough to still avoid clipping...

I use this exact signal chain as my main recording setup — low-sens AT-853s > 12v battery box > A10 set to line in — and have not had problems with hiss. And a level of 22 for solo electric seems pretty reasonable from my experience, so I doubt a bad battery is to blame.

In short: I dunno, man, that's weird.

Can you specify - do you use the "audio in" or "mic in" setting?

[depp91]

I've been having this problem too with my A10! I'm assuming the A10 has a bad S/N ratio (or at least mine does). I tested my SP-CMC-4U > SP-SPSB-10 setup into my D10 and there's zero hiss.

Have you been able to find a solution?

[vibrioidxire]

I was able to mediate it somewhat by cleaning my contact points with rubbing alcohol and a microfiber cloth and making sure that my recording is at a good setting so that I wouldn't have to do much amplifying and bring out the hiss. Other than that, I don't have the best solution to offer :-(

[morst]

Test the rig on something that doesn't matter at a similar volume level, like with a detailed studio recording played back on a decent stereo system at moderate volume.

[nulldogmas]

Can you specify - do you use the "audio in" or "mic in" setting?

"Audio in."

[depp91]

I was able to mediate it somewhat by cleaning my contact points with rubbing alcohol and a microfiber cloth and making sure that my recording is at a good setting so that I wouldn't have to do much amplifying and bring out the hiss. Other than that, I don't have the best solution to offer :-(

Have you tried recording with the mic-in setting instead of audio-in?
That's what I want to do next time but I'm a bit fearful that I won't be able to lower the levels enough in order to avoid clipping...

[unidentified]

Perhaps consider replacing the battery box with a pre-amp.