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Chrispire 26 October 2016

Hi all,

I'm helping to mix a meditative recording that consists mainly of bowed Tibetan singing bowls. Examples coming up momentarily...

The trouble we are having is that some of the deeper tones seem to pile up on one another to create apparent distortion. Thing is, I'm not sure if it really is "distortion", or just the natural way that certain frequencies interact with one another.

What's making this extra confusing is that this so called "distortion" sounds very different depending on what we use for monitoring. On my Event Opals there is no obvious distortion. At quiet volumes (which is how this music will be experienced) it's soft and relaxing to the ear. Listening on my Sennheiser HD 25 headphones sounds similar, but listening on my Shure SRH 1840 headphones reveals some pretty gnarly and unpleasant distortion sounds.

I'd LOVE to know how this sounds to you on your monitors/phones.

These short samples illustrate the problem. On my Shure headphones the distortion becomes quite apparent around the 18 second mark:

https://s3.amazonaws.com/audio-file-transfers/SB-Distortion-Test-1.wav

Here's another one. Distortion sounds when the second bowl kicks in at the 9 second mark.

https://s3.amazonaws.com/audio-file-transfers/SB-Distortion-Test-2.wav

This is making me unsure as to whether or not my headphones are faulty, or if they are simply revealing a genuine problem. There is no actual digital or analog distortion in the signal chain and no effects processing in use.

The tone of the bowls is fairly simple - they are almost just oscillating sine waves, and I'm wondering if that is the problem. The exact same notes played on a more harmonically rich instrument, like a piano for example, sound but totally distortion free. Are the singing bowls simulating harmonic distortion or sum/difference tones or am I just overreacting?

I'm rather confused at this point because I'm not sure if I have an unsolvable mixing problem or an equipment problem, or some other weird psychoacoustic problem. It would suck to have to throw out this whole recording simply because the nature of the instruments makes them impossible to mix without certain note combinations sounding distorted. This experience is really made me paranoid about releasing music that might sound awful on certain headphones. Again, I'd LOVE to know how this sounds to you on your monitors/phones and any other thoughts you might have.

Cheers!

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Comments

Sean G Wed, 10/26/2016 - 01:44

Hi Chrispire...welcome to RO !

Members here really do not like clicking on outside links for fear of picking up something malicious from a link they are not familiar with.

Whilst your link may be harmless, you will find that this is the case as a rule of thumb here. Its nothing against you personally, just a security thing more than anything to protect ones' self against malware.

There is an "Upload A File" button here (located at the bottom of the page next to the "Post Reply" button ) where you can upload a sample in Mp3 format at 320 kbps to the player here...unfortunately it doesn't support WAV files and your audio quality will not be as good as the original, but you may well find you will get a better response to your query that way and advice from those here who are only too willing to help.

I hope this helps. ;)

- Sean.

Sean G Wed, 10/26/2016 - 04:01

To be honest, I have only heard Tibetan singing bowls a few times...and have never had to record them.

From what I have briefly read these bowls are used for producing second and third harmonics...so it could be a case of harmonic distortion, but I would be guessing.

The first sample appears to sound like there is more distortion than the second to my ears. I am listening on Yamaha HS7 monitors in a fairly well treated room.

It may help if you can fill us in on how it was recorded, what mic, pre-amp etc and what was the environment like where it was recorded...was it treated or untreated etc.

Maybe someone here might be able to give some advice who may be familiar with these bowls or may have experience recording these or something similar.

audiokid Wed, 10/26/2016 - 14:29

Listening past the harmonics effecting other bowls or structures in the room, I do not hear anything concerning. They sound beautiful.
You mentioned the headphones distorting, not the Opals. I own Opals, love them but mine will fart at high volumes from sub freq.
Could it be that one of your headphones is also doing that? Reacting to a certain sub freq or codec flaw in a filter?

I'm not in my studio to upload this into my spectral analyzer, but I'm guessing there are some low sub freq in here. Did you use any HPF ?

Chrispire Thu, 10/27/2016 - 00:04

Sean and Chris, thank you very much for your replies. This situation has caused some stress and put the project into a stall until I could get some second opinions on the sound, so your assistance is greatly appreciated.

Singing bowls are interesting instruments that produce loads of harmonics in addition to their fundamental tone. In this project the bowls are played by stroking them with a wooden mallet that is covered in suede. This makes them produce a sustained tone with no transient, so they are great for drone sounds. The suede kills off the shrill scraping sound you would hear if raw wood was used against metal.

From memory these bowls were recorded very dry in a well treated space, closed miced with Omni Rode NT55's straight into an Apogee interface.

When you listen to these samples, you'll first hear a large bowl creating the deepest tone. You can also hear the whispy sound of the mallet as it circles the rim. That's part of the organic sound of the bowl and I kept that on purpose. The additional higher tones are from a bowl that I sampled to make it a playable melodic instrument. It was low passed and high passed so there's no rumble and none of that whispy sound. This leaves a pure fundamental tone that is pretty much just an oscillating sine wave.

I checked the audio samples in a spectral analyser and nothing erroneous was visible.

If I had to guess, there's no actual "distortion" happening, but what I'm hearing is the interaction between certain tones. For example, if you play a 100 Hz and 115 Hz sine was at the same time, you'll hear the resulting sound beating at 15 Hz. In the second music sample the deep bowl is playing a b-flat (116.5 Hz) and then the second bowls kicks in with an A-flat (207.6 Hz). The difference tone is 91 Hz - a tone that does not blend musically with the other tones that are playing in that moment. It's adding a gnarly texture that I don't like the sound of.

None of this is a surprise - this is just basic sine wave physics I guess, but the way I perceive the sound is SO different depending on what I listen with. Chris- just like you, when I listen on my Opals I do not hear anything concerning. They sound beautiful (thanks) and so even though the music can be dense at times with various low frequency notes playing together, there's nothing unpleasant about the sound. But when I listen on my Shure SRH 1840 headphones these "difference tones" are very pronounced and quite unmusical. They sound "distortionesque". This leaves me wondering:

(a) Are my headphones doing a fantastic job of revealing unpleasant tone combinations?
(b) Are my headphones doing a bad job by falsely exaggerating the sound of these frequency interactions in the music?
(c) If (a) is true, do I just accept that this is a natural part of the sound and leave it be? Is that an acceptable thing to do as a mixing engineer, given that the instruments have been recorded cleanly?
(d) If (b) is true, should I spoil myself and splash out on a new pair of Sennheiser HD800S headphones?(Truth be told, I did exactly that this morning. Sometimes you just need an excuse and this project gave it to me. So I'll have another headphone perspective on this music in a few days time). #silverlining

Boswell Thu, 10/27/2016 - 15:37

Chrispire, post: 442666, member: 50059 wrote:
(a) Are my headphones doing a fantastic job of revealing unpleasant tone combinations?
(b) Are my headphones doing a bad job by falsely exaggerating the sound of these frequency interactions in the music?
(c) If (a) is true, do I just accept that this is a natural part of the sound and leave it be? Is that an acceptable thing to do as a mixing engineer, given that the instruments have been recorded cleanly?
(d) If (b) is true, should I spoil myself and splash out on a new pair of Sennheiser HD800S headphones?(Truth be told, I did exactly that this morning. Sometimes you just need an excuse and this project gave it to me. So I'll have another headphone perspective on this music in a few days time). #silverlining

Hi Chris,

I don't think you have a distortion problem with your recordings, but I think you are capturing only part of the sound of each bowl. If you were to look at a slow-motion film of the vibration of a bowl rim, you would see not only the expected fundamental frequency plus low-order harmonics, but also nodes and antinodes moving slowly round the circumference (precessing), and it's these that give the pulsing or throbbing sound. Think of a toy gyroscope slowly rotating its near-vertical axis around the pivot point while the contained flywheel spins much faster.

I've been amplifying (for PA) and recording singing bowls over the last 10 years or so, and the main thing I have found is to make sure you pick up the spatial distribution of the sound from the bowl due to the precessing nodes and antinodes. I made many experiments before settling on using a pair of dynamic microphones set at 90 degrees to one another, both microphones horizontally level with the rim aimed at (and equidistant from) the centre of the bowl. The distance (radius) of the pair from the bowl is then your variable that you have to adjust and set according to the resonant modes of that bowl that are excited by the particular pujol technique used by the player.

The two microphones form an X-Y signal pair that can be sent direct to L and R channels of the recording or else processed by techniques such as M-S to generate elaborate sound fields. The straight L-R send can be a bit violent, so some form of channel interaction is usually needed.

It's a fascinating and much under-explored topic.

Chrispire Thu, 10/27/2016 - 22:21

bouldersound, post: 442680, member: 38959 wrote: I put them through my spectrum analyzer and the energy is concentrated at 120Hz and to a lesser degree some higher frequencies below 500Hz. I don't hear or see anything that suggests distortion, just the interaction of the tones.

Thanks bouldersound for taking the time to do this. P.S. If you are the Boulder Sounds sampling guy, I have a few of your libraries and enjoy them greatly.

Chrispire Thu, 10/27/2016 - 22:35

Boswell, post: 442695, member: 29034 wrote: Hi Chris,

I don't think you have a distortion problem with your recordings, but I think you are capturing only part of the sound of each bowl. If you were to look at a slow-motion film of the vibration of a bowl rim, you would see not only the expected fundamental frequency plus low-order harmonics, but also nodes and antinodes moving slowly round the circumference (precessing), and it's these that give the pulsing or throbbing sound. Think of a toy gyroscope slowly rotating its near-vertical axis around the pivot point while the contained flywheel spins much faster.

I've been amplifying (for PA) and recording singing bowls over the last 10 years or so, and the main thing I have found is to make sure you pick up the spatial distribution of the sound from the bowl due to the precessing nodes and antinodes. I made many experiments before settling on using a pair of dynamic microphones set at 90 degrees to one another, both microphones horizontally level with the rim aimed at (and equidistant from) the centre of the bowl. The distance (radius) of the pair from the bowl is then your variable that you have to adjust and set according to the resonant modes of that bowl that are excited by the particular pujol technique used by the player.

The two microphones form an X-Y signal pair that can be sent direct to L and R channels of the recording or else processed by techniques such as M-S to generate elaborate sound fields. The straight L-R send can be a bit violent, so some form of channel interaction is usually needed.

It's a fascinating and much under-explored topic.

Thanks Boswell for your detailed reply. You are spot on. When the bowls are played with this suede wrapped mallet most of the harmonics are muted so they don't really show up much in this recording. The low passing I employed to create a playable instrument removed what was left of the higher harmonics of the higher pitched bowls. In the larger context of this composition as a whole it works, but it's not something I'd normally do.

My approach to recording bowls is usually quite similar to yours. Sometimes I do like to use omni mics when I want to get a really "what it sounds like in my hand" up close and personal sound of a particular bowl without any proximity effect problems. As you said, recording singing bowls is a fascinating topic. Critical listening of singing bowl recordings often gets me thinking "deeply" about the nature of the sound they produce and how all the harmonics are working together.

Chrispire Thu, 10/27/2016 - 22:51

Conclusions...

My Shure SRH 1840 headphones are the culprit here. I just received delivery of a new pair of Sennheiser HD800S headphones so I've had the opportunity to listen to the music on (1) Even Opals, (2) Sennheiser HD25-1 II phones, (3) HD800S phones, (4) iPhone earbuds and finally my Shure SRH 1840 phones.

I've had the Shures for about 3 years and they have been a great tool for forensic listening. But I think I've found one of their weaknesses. Assuming that they are not inherently faulty, they definitely struggle to produce certain low frequency tone combinations and were presenting some grinding, burred distortion sounds to me that I do not hear anywhere else.

So this day ends happily thanks to your help and also to these amazing new headphones. Without meaning to turn this thread into a product review, I have to say "Holy S#*@" these things sound amazing. I've held my Shures in high regard since I bought them, but they sound like rubbish in comparison to the Sennheisers, which are an utter revelation. I love it when the marketing hype around a product actually matches up with reality. I think I'm going to be kicking back this weekend and just listening to a lot of music.

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