Audio Limitations of the XL-H1

[Brian Findlay]

Hi All,
Thought you might be interested it this, probably won't effect most of you, but worth knowing if you run into it.

One of the reasons I bought an XL-H1 was for time codes output to run a dual system. I have a Tascam HD-P2, a great digital recorder that uses Flashcards.. it does 24bits up to 192K..and yeah..it does make a difference if you have musical content. Anyway, I run caridoid mics (shotguns, whatever) to a mixer Shure FP24, out of the FP24 (XLR line level) to a balanced splitter, one output of the splitter goes to the HD-P2, the other goes to the XL-H1. Both the FP24 and he HD-P2 are very high quality, and are capable of great sound with a very good S/N ratio, etc.

One of the things to be gained from such a setup is that most prosumer cameras have really poor audio input amps, and generally less that great sound is the result. One way to get mitigate this is to keep in the camcorder inputs gain down low, and use the high quality amp (FP24) to boost the signal. Or in my case, record externally and use the XL-H1 soundtrack to help sync the final product visually.

As I haven't had this camera very long, I am still very much in the experiments stage, but I had done several recordings with another camcorder with very good results this way (sony HVR-A1U)..

When I monitored the inputs (carfully making sure that nothing was in clipping).. the input of the XL-H1 behaved very strangly (I used manual gain of course).. I tried a varity of settings line/mic Attenuation On/Off, and the same problem was seen everywhere.. first, the input seemed to limit in most cases, what was going in.. but even when I decreased the input levels, I would get a bad (echo like) sound on the recording.. with very little control over the levels, they just didn't behave like they should. The HD-P2 however, sounded fine.

I contacted Shure first, they informed my that they have seen this before with other prosumer cameras..as they put it something like "with inferiour input designs, not really balanced, impedance matched" and then I contacted canon.. and asked them the same question..

Canon's response was the following:
------------------------------------------------>
Dear Mr. Findlay:

Thank you for your inquiry. We value you as a Canon customer and
appreciate the opportunity to assist you. I'm sorry to hear that you
are experiencing audio difficulty with the XLH1 camcorder.

Nothing in any of the posted Canon specifications or literature would
indicate that the XLH1 is impedance matched. This would lead us to
believe is not. If you have the levels set properly and you are not
overdriving the input signal, then it is most likely that you are
having an impedance irregularity. This being the case, I would suggest
referring to your work around plan.

Please feel free to contact us again if you have any other questions or
concerns about the XLH1 camcorder.

Thank you for choosing Canon.
--------------------------------------->

Note.. the work around was what shure suggested, which was to buy some inline XLR transformer matching XLR adaptors that you conect the XLR cable to before connecting to the Canon ($65 each).

I don't mind doing this. It just one of those things where you know it wasn't the extra $20 it would have taken to do this right, its just that I think they purposely make their audio inferiour so as not to pressure their upper models... Just wish they would try to do it all right. It's just another couple more pieces of junk that you have to have (and lose at some critical time)..etc.

[Dan Keaton]

I suggest that you run a test without the splitter, and thus without the HD P2. Use Line Out of the mixer to Line In of the XL H1.

If you do run the test, please let us know the results.

[A. J. deLange]

The XL_H1 manual clearly states on the specifications page that the XLR inputs are 600 ohms and the audio path diagram clearly shows baluns in the XLR circuits. 600 Ohms is the standard impedance for an unbalanced audio circuit going back to the earliest days of telephony. Furthermore, an impedance mismatch is usually not a problem at audio frequencies unless cables are long enough that the round trip time of an echo is noticeable or the output impedance for the source is much higher than the input impedance of the sink. If, for example, a source with 900 Ohm output impedance were connected to a device with 100 Ohm input impedance only 1/10 of the voltage would transfer representing a 20 dB loss. The input impedance for the Tascam is 1.3K while the output impedance of the FP24 is 120 Ohms (it is common practice to have low output impedance and high input impedance to minimize coupling loss as explained above). Thus the FP24 matches neither the XL-H1 nor the HD-P2.

What's in the splitter? Is it transformer coupled? How about the matching devices you bought? Input and output impedances for those?

[Brian Findlay]

I've tried a variety of ways..nothing much seems to make much of a difference. The splitter itself has one output direct, and the other goes through a transformer. I've tried outputs both ways to the XL-H1 and the the HD-P2, no real difference.

On the input of the XL-H1 I tried Mic in (no Attenuation), Mic in (Attenuation), Line in, Mic in (with a 40db pad), Mic in (with Atten on and a 40DB pad), all produce nothing very good as a result. The more attenuation you use, the less the echo chamber effect, but nothing I was really totally happy with.

I think what was the most surprising for me was that by all accounts the meters were reading that the signal was maybe half scale, yet the sound was terrible.

I worked with audio systems over a decade ago.. I used to repair profesional PA systems, mixing boards, etc.. I was an analog engineer, I designed mostly switching power supplies, not much audio then. I understand impedance measurements and how loads can be critical. That was some good detective work..A.J.D thanks.. I'm getting slow in my old age.. I should have done this as DD.. instead I picked up the phone to call field support ;-) (bad customer).

But no matter, I'm just really surprised by this difficulty.. I mean 12 bits resolution is pretty poor, one of the things you give up for HDV. So I can't help think I'm the only person doing this. Given another camera HVR-A1U which by all accounts is a consumer camcorder could do this with no problem.. I'm dissappointed.. As an engineer, you have to try to antisipate how and for what people will use things, and make some compensations.

I'm not trying to bash the camera, I would buy it again, I think the visual results I can achieve with it are just stunning. But I stand by my opinion that the audio was pretty poorly designed. It is worth mentioning, that the two mics I was running (a Sennheiser K6/66 and Tram TR50 sound okay (not great, but okay) when they are direct in.

It is also worth mentioning that the "echoy" effect can be heard with nothing but the mics attached when you compare the sound to the HD-P2, but I doubt anyone would really notice this unless you were doing a side to side comparison (comparing 12 bits to 24 yes, but there is something more than that going on). Its just this effect is magnified when used in this situation.

I used to own a distortion analyzer and a low distortion flat sign wave generator.. I would love to hook it up and record the low distortion source and then play it back into the distortion analyzer. I would personally bet that inexpensive digital recorder from radio shack would beat it.

I'm not trying to intentionally irritate anyone, but I realize that saying such things about this camera on this board may not be popular. Still I think it should be said if you are really trying to evaluate this camera.

If there is anyone out there who does have access to this gear, *PLEASE* spend the time and run this experiement. I really would like to know, you know that if I am right, canon would never publish this info.. and if I'm wrong you can smugly call me an ass -;)

Thanks!

Brian Findlay

[Christopher Glaeser]

Originally Posted by Brian Findlay

So I can't help think I'm the only person doing this.

Hmm, it's possible you are the only person doing this. Sorry for being so dense, but why are you splitting/recording audio on two devices? Is it to sync the video with the HD-P2 audio?

Best,
Christopher

[Dan Keaton]

Dear Brian,

From reading your post, you have tried connecting the microphones direct and the sound is better but not great.


You mention that the sound is 12 bits. I believe that this is incorrect.

Are you recording in SD or HDV?

In SD you have the choice of two channels, each 16 bits/48k PCM.

If you use four channels you will use 12 bits/32k PCM.



In HDV, the MPEG compression used to record audio depends on whether you are recording 2 channels or 4 channels.

The following is how I read the Canon XL H1 specifications from page 152 of the English manual.

HDV 2 channel:

MPEG-1 Audio Layer 2, 16 bit/48k 384kbps

HDV 4 Channel:

MPEG-2 Audio Layer 2, 16 bit/48k

[Brian Findlay]

Dan, You are right.. I stand corrected, I'm not sure where or why, but I had this misinformation in my brain for some time, its nice to get it corrected.. my humble apologies for the mistake.

Please don't think I am being hyper critical when I say the difference is easily heard, I have tinnitus (a permanent ringing in my ears), and I can hear a marked difference between the recording on the 24 bit and the XL-H1. Without prompting, I have also questioned my girlfriend, my son, and daughter.. all can hear what I hear with my (defective) ears. I suppose its possible that there is something wrong with just MY XL-H1. But like I commented before, with the mics straight in, its really only perceptible in a side by side comparison with the 24 bit recording. Where does the problem lay? Operator Error? Higher distortion? I don't know, I did find some interesting comments on the web regarding compression, that described the compression as producing a "fuzzy sound".. could their fuzzy be my echoing? I also in fairness found information that described the difference between compressed and uncompressed audio as imperceptible, though I really don't believe this unless it's lossless (which I don't know).

Anyway, I'll let it rest at this point. I really would like to find someone with test equipment to do a distortion test, because at this point, that (to me) seems to be the most logical. I read an excellent book about a year ago by Jay Rose called "Producing great sound for Digital Video", where he did this test for several pro-sumer (God I hate that word) cameras from all the makers. Unfortunately the testing was done about 2 years ago and most of the cameras are not currently manufactured. I believe he sighted the poor cabling in the shoulder rest of an earlier model Canon as being a great source of noise. Almost all had really high distortion, and I think this is what I have run into now. I don't know where the book is at this moment, but I wish I had it for reference.

Why do I try to record like this? Several reasons.. Even though I bought the canon for the time codes, I have yet to use it with the HD-P2.. so I have been lazy and lining up the video and the audio by sight in FCP.. Pattern recognition in human beings is a wonderful thing. Second, as I have done in other recordings, I listen to both recordings (camera and HD-P2), if the the HD-P2 is clearly superior, I will use the HD-P2. If not, then the original track. As I had done this with a Sony HVR-A1U before, I found only a few times (primarily music), where it was really improved. But, this last recording I did with the XL-H1 was just in a normal interview, talking only. And it was noticeable in an A to B comparison of just straight in audio to the XL-H1 and the HD-P2. So if anyone else has a good quality digital recorder, mixer, and mics and they want to do this experiment, please do and tell me what you think. If you tell me you can't hear a difference, maybe I'll send my XL-H1 in for a check up. At this point however, I tend to think the problem is more systemic as its not really broke and its on both channels (always possible a common regulator or filter has gone...but)

Thanks All

Brian

[Dan Keaton]

Dear Brian,

Nice Post!

In my humble opinion, a good quality recorder that records at 24 bits, such as the TASCAM HD-P2 or the Sound Devices 7 series, will always sound better than a 16 bit recorder. I have not specifically tested this, but I believe that the 24 bit recording will be audibly better.

Since you are using a splitter, which means that you are physically tied together via cables, I would recommend going into the HD P2, then line out to the XL H1. This would eliminate the splitter.

I am most certain that the audio preamps in the Sound Devices 7 series are better than the preamps in the XL H1. I expect that the audio preamps in the TASCAM HD P2 are probably superior also.

Since it is fairly easly to line up the audio, in these circumstances where you have the same audio on both the camera's and recorders tracks, why don't you just use the HD P2 audio?

I purchased the Sound Devices 744T prior to, and in anticipation of purchasing the XL H1. For non-critical work, I just use the camera's sound system. For critical work, I use both. backups are nice.

Frank discussions of problems help us all learn. I did not find any of your posts hyper-critical. I do feel that most of your problems are in the splitter and in the inherent differences between 16 bit and 24 bit sound.

The Canon XL1s had noisy mike preamps; one could hear hiss at normal to higher gains. I used a Beachtek DXA-8 to solve the hiss problem. While I have not tested the XL H1, I think that it also benefits from an external mic preamp.

I hope this has helped.

[Brian Findlay]

I've torn down everything and am in editing hell until two weeks from now when I have a small showing. I'm going to try the RCA jacks as inputs and see what that yields.. It would be pretty funny if it really works.. especially after dropping several hundred in high quality cables and splitters. But I've really gotten the idea that the XLR inputs are just for show as opposed to being a really higher quality interface.. I guess they at least lock your cables in, something that RCA jacks won't do.

I have a brain like a sive, but I'll try to remember to post the results when I get time in a few weeks. BTW: I didn't think I'd ever be interested in the 744T, but have run into 2 ocassions in the last month where I really could have used 4 channels. A very nice box from the looks of it.

Thanks!

Brian