Hi, I’ve just gone from analogue aids (phonak superfront ppsc) over to digital (unitron Max e sp) and was struggling with speech warble, which was compromising speech understanding. I searched the internet, phoned the manufacturer and changed audiologists (took 7 trips all up!) . Finally found a post on here about it and my new audi did the feedback control cancellation that was suggested and the warble is gone. It was awful, sounded like someone talking through a fan (or a Dalek from Doctor Who!). Now the warble is gone, my Audi is keen to know whether others have had this issue and do you think frequency compression plays a part as well? One of my aids is set up with no compression and the other is 1:1 so we can try to figure out if that was a contributing factor.
I will also add, I have never found a digital hearing aid that sounds so good!
Did you say that your new audi enabled the feedback manager for you? Or cancel/disable the feedback manager feature for you?
She cancelled the feedback control, so it is completely turned off now.
OK, that’s what I figured. There are really 3 feedback strategies that are commonly employed. Phase shifting, frequency shifting (by a small amount, as to supposedly not be noticeable), and gain reduction in resonant frequency areas where feedback occurs.
Most likely culprit for the warbling you experienced is the frequency shifting strategy. I’ve seen several cases on this forum where people reported hearing fluttering/warbling, especially on single tone sounds, but also on speech. In almost all these cases, it seems like cancelling the feedback control removes the issue for them, like in your case. But for the vast majority of people (me included), it’s not an issue for them. It seems like people who are musically minded tend to notice the fluttering/warbling more. But I’m inclined to think that I’m musically minded as well, but I generally don’t detect it. So it seems to be on an individual basis. Maybe depending on the type of hearing loss.
Frequency compression is a whole different animal altogether. It’s done to move sounds in the high frequency areas (where significant loss tends to occur) to lower frequency areas where loss tends to be less significant so that those high sounds can be heard better, albeit at a lower frequency.
It was very strange indeed, I got 3 ‘normal’ hearing people to put the aid in and they all couldn’t believe how significant the warble was, it was impacting speech so terribly. So thankful I’ve managed to get the aid sounding clearer now. Only getting a slight whistle when I cover the aid now, I can love with that though!
On the Oticon OPN, they only shift the frequency by 10Hz. I wonder how much shifting they do in your Unitron Max? I would think that the bigger the shift, the more warbling it creates.
The warbling occurs when you hear both the original unamplified sound through the vent and the amplified frequency shifted sound on top of it. Let’s say if it’s a pure tone, there’ll be two sinusoidal waves slightly out of sync presented to your hearing.
If you draw these sound waves out on paper, you’ll see that there is an overlapping area where one sound wave cancels or diminishes the other momentarily during the shifted amount, creating this warbling/fluttering effect. The larger this shifted region is, the more pronounced the effect become noticeable.
Thanks for that awesome explanation, I’ll fill my Audiologist in next week when I see her again and ask about the Unitron frequency shifting.
I’m hearing great things about the Oticon Opn (from professionals, not consumers as yet) so I’m keen to try them out for myself.
I used to have this issue when performing on wind instruments. My audiologist turned off the feedback manager and that helped. Unfortunately, with the feedback manager off had to have my gain lower and didn’t hear generally as well. Finally found a manufacturer where this is not an issue. With the Widex Beyond 440 hearing aids I have no warbling distortion and can keep the feedback manager on. Best sound for me in decades.
I’ve heard great things about that 440 aid as well, I’m currently going through bloom hearing centres who are owned by Widex so possibly move to a Widex device next time. One thing I’ve noticed with the Unitron Max E SP I have currently is, the microphone is very close to the hair line so I can hear my hair scratching on the aid all the time, not really a huge issue as it’s up most of the time in a ponytail anyway. Speech sounds pretty awesome now but background noise is very quiet (one example is I’m currently at a family members holiday house on the River Murray and can’t hear the birds like I usually can, they’re very quiet and distant sounding). Again, minor things but all up I’m really pleased with the speech sound quality compared to other digitals I have trialled in the past 15-20 years (Bernafon, Siemens, Oticon).