[WXC/VFX] Voicemail codec quality.

Forums › One New Zealand (including Vodafone, WxC, Farmside) › [WXC/VFX] Voicemail codec quality.

jpollock

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#13836 31-May-2007 10:07

Hello,

I've got my voicemail forwarded to my email account. Great stuff. I have a couple of feature requests/problem reports:

1) I'm noticing that the quality of the recording is very, very poor. There is a lot of staic, and a lot of crackle/pop (snaps over top of the voices). Is it possible to increase the bitrate of the .wav? Perhaps if you could increase the bitrate of the .wav and convert it to an mp3 if you are concerned about bandwidth?
2) I would love to have a link in the mail allowing me to delete it out of my mailbox when I click it.
3) I would love to be able to send the voicemail to multiple email addresses. I currently do this on my own server, but it was a bit of a pain in the ass.

I love the voicemail service! It allows me to track my messages from work!

Jason

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grant_k

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#72969 31-May-2007 10:22

jpollock: 1) I'm noticing that the quality of the recording is very, very poor. There is a lot of staic, and a lot of crackle/pop (snaps over top of the voices). Is it possible to increase the bitrate of the .wav? Perhaps if you could increase the bitrate of the .wav and convert it to an mp3 if you are concerned about bandwidth?

I use this function too and find it great.

However, I think you are blaming the wrong device here...

By listening to the recording on a PC, you are hearing all the high-frequency stuff (clicks, pops etc) which are barely noticeable on a phone handset which typically doesn't reproduce sounds above 3.4kHz.

It is the originating phone handset and cradle switch that is the source of all these noises. I find that callers voices are frequently distorted with a raspy edge to the sound, but that is a function of the cheap and nasty microphones used in phone handsets.

Older phones used to have Carbon Microphones which were really bad -- are they still used nowadays? If not, then I suspect that the microphone type will be Electret Condenser which still gives pretty RS quality. The best type of mic is dynamic, but it needs extra electronics to boost the signal. Cyril will probably know which type of mic is commonly used in phones these days.

Increasing the sample rate of the WAV file will make these problems worse, not better. In order to listen to voice mail, you really need a low-pass filter with a cutoff frequency of 3.4kHz, then it will reproduce the recorded message much the same as a phone handset does.

jpollock: 2) I would love to have a link in the mail allowing me to delete it out of my mailbox when I click it.

AGREED!!! That would be an awesome idea

At present I have to remember to dial *62 on my phone and delete the messages after I've listened to them on my PC.

maverick

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#72970 31-May-2007 10:25

Hi Jason,

Could you send me a copy of the voicemail message so I can take a listen as voicemail via email should be pretty good , so I would like to hear what you are getting.

MP3 not really relevent at this stage as the .wav file should be a good quality

Deleting directly from the Email, sorry not possible att this time, it's just a Carbon Copy from your Mailbox

Multiple EMail address, yes been a feature request for a while now,

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Niel

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#72975 31-May-2007 10:37

To add the what is already said, if you convert from one audio compression to another then you also increase the possibility of noise depending on the quality of the conversion program. With digital processing there are things like interference patterns and for example noise at a high frequency can actually convert to noise at a low frequency if not done 100% correct. I had a problem with Bluetooth headphones (not headset, but proper headphones) where there was distortion with some types of music but not with other types of music. And these were not cheap headphones, it was simply digital noise due to one CODEC interfering with another. So changing to MP3 will not improve quality, it is best to stick with the native CODEC.

My recording is fine (but have done only one).

It is unlikely you will find anything other a condencer mic in a handset. As for quality of a condencer mic, reference microphones are condencer mics. They are excelent, however the quality is largely influenced by the way it it mounted. (I am an electronic engineer as well as a part time sound engineer.)

You can never have enough Volvos!

grant_k

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#72982 31-May-2007 10:53

Niel: As for quality of a condencer mic, reference microphones are condencer mics. They are excelent, however the quality is largely influenced by the way it it mounted...

Yes, fair comment Niel, I have used those reference microphones with Pink Noise Analysers too, and you're right, they are capable of excellent performance if mounted correctly. Unfortunately, most telephone handsets are anything but

jpollock

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#72988 31-May-2007 11:17

I was assuming that there was some transcoding already being performed on the VM platform (to explain the pops), with storage/bandwidth being the reason. That was why I requested mp3 instead of .wav. I thought that it would allow a higher quality recording to be saved, at the cost of some CPU for the transcode.

However, it looks like it is a straight dump of the network PCM data. I assume the network is using G.726 since it's ADPCM instead of G.711? As everyone pointed out, transcoding the raw traffic would not result in a better result. :)

See, I'm not a total nub. ;)

Just to let everyone know, I've been shifting between PCs (and tried a couple of other players), and the problem seems to be really dependent on the playback tool.

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grant_k

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#72995 31-May-2007 11:47

jpollock: I assume the network is using G.726 since it's ADPCM instead of G.711?

The default Voice Codec is G.729 which gives a reasonable compromise between bandwidth and quality. If you send a fax, the G.711 codec is used.

I also have an older VoIP system using H323 protocol and G.726 codec. VFX with G.729 definitely sounds better (quantisation noise is not so raspy).

jpollock: Just to let everyone know, I've been shifting between PCs (and tried a couple of other players), and the problem seems to be really dependent on the playback tool.

I always used WMP for playback and find that the quality varies greatly depending on the type of phone used by the Caller. If it's a mobile, it's usually pretty bad, some of the better wired phones are actually quite good to listen to.

maverick

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#73021 31-May-2007 14:13

Hi Jaon,

Thanks for the PM, I took a listen to all 3 messages, all sounded good to me using windows media player, I also had the TUANZ confernce streaming and running some database queries so my CPU usage was high, still sounded good, I also tested them all on 4 different machines also sounded clear and fine...btw don't foget to call LV Martin

So my thoughs are your playback device is probably causing the bad quality as I am listening to exactly the same message as you are and it sounds great, if you have no objections you could post one or all of the links here and we can get some feed back from other users using different playback devices ?

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jpollock

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#73051 31-May-2007 14:59

Here you go.

http://www.pollock.ca/~jpollock/vm.wav
http://www.pollock.ca/~jpollock/vm2.wav
http://www.pollock.ca/~jpollock/vm3.wav

What I've found:

Sounds like it's a problem with the xine codecs. They seem to turn the clipping static into a loud pop.
Windows Media Player doesn't have a problem.
mplayer doesn't have a problem. I assume that this is because they are using the same codec as WMP. :)
noatun doesn't have the problem as badly.
xmms refuses to play them at all.

Sounds like it's just a problem with xine. I'll raise a fault with them once I track down their bugzilla system. :)

In the meantime, I've changed my system to play .wav's through mplayer instead of any of the other media players I have.

Sorry, I made an assumption that my system would reliably play back a wav file. Guess it doesn't like the ADPCM that much.

Jason

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maverick

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#73055 31-May-2007 15:14

No problem Jason, it happens first option is to look at the most logical option first, we like to help and it's an interesting topic someone else may experience the same thing when using different playback devices so this type of discussion is very beneficial to the community and to ourselves as well.....and as long it's not a Network problem I'm happy

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grant_k

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#73056 31-May-2007 15:21

All 3 messages play OK for me in WMP with no crackles or pops.

However, the second message ...vm2.wav from LV Martin has quite a raspy edge to it, typical of a cheap/nasty phone handset, and/or someone hollering down the phone at too loud a volume.

We have had many recorded messages like this, but also, we have had many that are as good or better than the ...vm1.wav and ...vm3.wav messages. Like I say, it all depends on the caller's phone, speaking volume and sometimes, the line quality.

Certainly it looks as though WMP is a pretty safe bet for playing back any messages recorded by VFX.