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Audio compression does not even give FM quality
I just did an experiment using OGG Vorbis to encode the Choral Evensong from
the FM broadcast of Radio 3 to check out how good the codec is. I passed the Radio 3 line output from my AV amp into the ADC of my Sony Minidisc Deck and connected the digital output of that to the SPDIF input of my PC where I recorded the signal. I monitored the live station using the headphone socket of the MD deck so as to ensure that the levels of the signal I was going to record and the playback signal were both at the same level. I made 5 recordings at 112 kbps, 128 kbps, 192 kbps, 256 kbps and 44 KHz PCM uncompressed. All of the recordings that I made using OGG were instantly distinguishable from the live radio signal and the PCM uncompressed recordings except for the one at made at 256 kbps. I could perceive the difference between the compressed file and the live signal instantly at 112 kbps, within 10 seconds at 128, within 20 seconds at 192 and only at 256 kbps did I have to play the sound back twice and compare it directly to the uncompressed PCM file. The reason why the compression was easy to tell is due to the fact that the echo in the church that Radio 3 Choral Evensong is broadcast from is almost impossible to encode at bitrates below 256 kbps and when compressed at these bitrates it sounds like someone who is breathing helium inside a diving helmet. This helium effect becomes less pronounced the higher the bit rates go until you get to 256 kbps where you don't notice it. Unfortunately even are 256 kbps the low hiss and electrical interference sound on the Radio 3 signal cannot be encoded properly and the tell tail squelching mud and hissy echo distortion can be picked up within 10 seconds when you alternate between playing back the uncompressed recording and the compressed recording. Once you have picked this distortion up and know what to look for then you cannot miss it no matter how many time you play the OGG file back. I also encoded a classical music file I extracted from CD using OGG and although it is passable even at 64kbps owing to the studio quality of the recording and the file being purly instrumental, the very low levels of hiss are uncompressible at this bit rate and are a giveaway to compression. All you need to look out for is a hissy echo and a very high pitched pinging sound. The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. The fact the ogg can't even encode hiss properly at 256 kbps the equivalent of mp2 at 1024 kbps means that mp2 can not even approach FM quality PCM even if is sampled at the same bit rate so why was it ever devised when FLAC can give you completely lossless compression at 512 kbps ! In fact even the biased creators of mp2 and the EBU claimed that mp2 was transparent at 256kbps per channel or 512 kbps but mp2 is lossy at this bit rate while FLAC is completely lossless. Further more why was NICAM ever devised when FLAC uses less bandwidth than NAICM which only uses 12 bits. On top of this if FLAC were used on DVB instead of mp2 using 64 QAM modulation correct me if I'm wrong but wouldn't it use the same bandwidth as mp2 at 128 kbps on DAB and be completely lossless and better than FM so why was DAB even chosen over FLAC in the first place ? |
Audio compression does not even give FM quality
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Audio compression does not even give FM quality
housetrained wrote:
That's why I'm so disappointed in DAB radio. All seem in only 128kps! Rubbish! 98% of stereo stations on DAB in the UK are 128kbps: http://www.digitalradiotech.co.uk/worldwide_dab.htm -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Please sign the petition asking the BBC to provide better audio quality on its radio stations on DAB, Freeview, satellite and cable: http://tinyurl.com/a68e4 |
Audio compression does not even give FM quality
Agamemnon wrote:
[snip] Ogg isn't designed to target bitrates, but quality levels. -q5 and above are worth using. However, you appear to be listing the CBR bitrates you used. This suggests you don't know how to use the encoder properly. The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. Arguable. I can think of one test result that could "prove" your point, but the AAC encoder in that test is a-typical. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Arguable. Actually, I think you'd struggle to back this one up with any published test. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps This is just silly reasoning. It doesn't work like that. which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. Even freeformat mp3 stops at 640kbps. Try it - for some things its "near lossless". The fact the ogg can't even encode hiss properly at 256 kbps the equivalent of mp2 at 1024 kbps means that mp2 can not even approach FM quality PCM even if is sampled at the same bit rate so why was it ever devised when FLAC can give you completely lossless compression at 512 kbps ! That argument is based on your faulty reasoning. Plus FLAC often needs over 800kbps (though probably not for Choral Evensong!) In fact even the biased creators of mp2 and the EBU claimed that mp2 was transparent at 256kbps per channel No, 256kbps stereo - i.e. both channels total bitrate. Further more why was NICAM ever devised when FLAC uses less bandwidth than NAICM which only uses 12 bits. Well, obviously because the inventors didn't have you knowledge and genius! ;-) (btw, the real answer is in the name: Near Instantaneous... FLAC isn't, neither does it deliver a guaranteed bitrate) On top of this if FLAC were used on DVB instead of mp2 using 64 QAM modulation correct me if I'm wrong I keep doing, but I doubt it'll help. but wouldn't it use the same bandwidth as mp2 at 128 kbps on DAB and be completely lossless and better than FM so why was DAB even chosen over FLAC in the first place ? There's one major problem with lossless compression in broadcast: you can't guarantee the bitrate. If you want near lossless, use NICAM, or something like Wavepack hybrid mode. It's useful in some situations, but a good lossy codec is a more elegant situation for one-time encoding and a limited bitrate situation. I'll turn the question around: what's wrong with AAC at 192kbps? Cheers, David. |
Audio compression does not even give FM quality
wrote in message oups.com... Agamemnon wrote: [snip] Ogg isn't designed to target bitrates, but quality levels. -q5 and above are worth using. However, you appear to be listing the CBR bitrates you used. This suggests you don't know how to use the encoder properly. Wrong. I was using ABR. The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. Arguable. I can think of one test result that could "prove" your point, but the AAC encoder in that test is a-typical. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Arguable. Actually, I think you'd struggle to back this one up with any published test. Based on my comparison between this and the MUSICM codec for Cool Edit Pro I have all the evidence I need. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps This is just silly reasoning. It doesn't work like that. which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. Even freeformat mp3 stops at 640kbps. Try it - for some things its "near lossless". Why should I bother when FLAC is completely lossless. The fact the ogg can't even encode hiss properly at 256 kbps the equivalent of mp2 at 1024 kbps means that mp2 can not even approach FM quality PCM even if is sampled at the same bit rate so why was it ever devised when FLAC can give you completely lossless compression at 512 kbps ! That argument is based on your faulty reasoning. Plus FLAC often needs over 800kbps (though probably not for Choral Evensong!) In fact even the biased creators of mp2 and the EBU claimed that mp2 was transparent at 256kbps per channel No, 256kbps stereo - i.e. both channels total bitrate. That's not what I read. Further more why was NICAM ever devised when FLAC uses less bandwidth than NAICM which only uses 12 bits. Well, obviously because the inventors didn't have you knowledge and genius! ;-) (btw, the real answer is in the name: Near Instantaneous... FLAC isn't, neither does it deliver a guaranteed bitrate) On top of this if FLAC were used on DVB instead of mp2 using 64 QAM modulation correct me if I'm wrong I keep doing, but I doubt it'll help. but wouldn't it use the same bandwidth as mp2 at 128 kbps on DAB and be completely lossless and better than FM so why was DAB even chosen over FLAC in the first place ? There's one major problem with lossless compression in broadcast: you can't guarantee the bitrate. If you want near lossless, use NICAM, or something like Wavepack hybrid mode. It's useful in some situations, but a good lossy codec is a more elegant situation for one-time encoding and a limited bitrate situation. I'll turn the question around: what's wrong with AAC at 192kbps? Same problem as with OGG at 192kbps I expect. Can't deal with moderate hiss, electrical and digital interference noises (more or less square waves) picked up by my FM tuner and speech echo. Is AAC any good at encoding square waves. Didn't think so. It wouldn't be very good at recording bird song and playing it back to the birds either. Cheers, David. |
Audio compression does not even give FM quality
Agamemnon wrote:
The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. Remember that audio is distributed to the FM transmitter sites via NICAM for the BBC stations and (apparently) usually 384kbps APT-X for commercial radio stations. NICAM is 14-bit 32 kHz sampling rate companded down to 10-bit. So your 1024kbps (16-bit, 2-channel 32kHz sampling rate) is overstating FM's audio quality by 2-bits per sample from the start, and the linear PCM bit rate going into the NICAM encoder is 896kbps. The compression part of NICAM consists of using 10-bit resolution for large amplitude samples, but keeping 14-bit resolution for small amplitude samples. MP2 will start to sound better than NICAM at some bit rate, and I reckon MP2 at 256kbps will sound better than FM. In which case, all the BBC TV channels' audio would be better quality than FM, but the BBC FM stations beat all the UK radio stations on all of the digital TV platforms and DAB. Hence the petition to get the BBC to increase their bit rates: http://tinyurl.com/a68e4 -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Please sign the petition asking the BBC to provide better audio quality on its radio stations on DAB, Freeview, satellite and cable: http://tinyurl.com/a68e4 |
Audio compression does not even give FM quality
"DAB sounds worse than FM" wrote in message ... Agamemnon wrote: The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. Remember that audio is distributed to the FM transmitter sites via NICAM for the BBC stations and (apparently) usually 384kbps APT-X for commercial radio stations. It might start out as NICAM for the BBC but what about commercial radio stations. Community radio stations usual broadcast direct so they would offer the best sound quality of all. NICAM is 14-bit 32 kHz sampling rate companded down to 10-bit. So your 1024kbps (16-bit, 2-channel 32kHz sampling rate) is overstating FM's audio quality by 2-bits per sample from the start, and the linear PCM bit rate going into the NICAM encoder is 896kbps. The compression part of NICAM consists of using 10-bit resolution for large amplitude samples, but keeping 14-bit resolution for small amplitude samples. MP2 will start to sound better than NICAM at some bit rate, and I reckon MP2 at 256kbps will sound better than FM. In which case, all the BBC TV Not on any decent surround sound system it wont. Anyone sitting near any of the surround speakers or the left and right front speakers can easily hear the high pitched whine every time someone speaks. On the other hand if we are talking about Dolby 5.1 in mp2 at the equivalent of 256kbps per channel then that's fine and an improvement just as long as you are not listening to a down mix on headphones where the distortion if there is any noise present is obvious. channels' audio would be better quality than FM, but the BBC FM stations beat all the UK radio stations on all of the digital TV platforms and DAB. Hence the petition to get the BBC to increase their bit rates: What is needed is for DAB to be scrapped and replaced with a better system and this can best be achieved by a complete boycott of DAB revivers and stations. After starting that protest off then we should demand that all BBC radio stations are broadcast in AAC+ using Dolby 5.1 encoding so that they can allow the listener to experiences DVD-Audio and SACD recordings. http://tinyurl.com/a68e4 -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Please sign the petition asking the BBC to provide better audio quality on its radio stations on DAB, Freeview, satellite and cable: http://tinyurl.com/a68e4 |
Audio compression does not even give FM quality
Agamemnon wrote:
"DAB sounds worse than FM" wrote in message ... Agamemnon wrote: The implications of this experiment to DVB are clearly obvious. OGG Vorbis is equivalent in quality to AAC and maybe even AAC+. OGG at 64kbps is equivalent to mp2 at 256 kbps ie. 4 times the bit rate. Thus for DVB to get anywhere near to FM it needs to be encoded at the equivelent of 4 times 256 kbps ie. 1024 kbps which is the same bit rate as sampling the 16 KHz FM audio signal in PCM at 32 KHz in the first place. Remember that audio is distributed to the FM transmitter sites via NICAM for the BBC stations and (apparently) usually 384kbps APT-X for commercial radio stations. It might start out as NICAM for the BBC but what about commercial radio stations. Community radio stations usual broadcast direct so they would offer the best sound quality of all. Can't you read? I said "usually 384kbps APT-X for commercial radio stations". APT-X is a lossy digital audio codec, and I would bet that NICAM sounds better. Put it this way, Radios 1-4 are easily the best sounding FM stations that I can receive. NICAM is 14-bit 32 kHz sampling rate companded down to 10-bit. So your 1024kbps (16-bit, 2-channel 32kHz sampling rate) is overstating FM's audio quality by 2-bits per sample from the start, and the linear PCM bit rate going into the NICAM encoder is 896kbps. The compression part of NICAM consists of using 10-bit resolution for large amplitude samples, but keeping 14-bit resolution for small amplitude samples. MP2 will start to sound better than NICAM at some bit rate, and I reckon MP2 at 256kbps will sound better than FM. In which case, all the BBC TV Not on any decent surround sound system it wont. I'm not interested in surround sodding sound systems. Anyone sitting near any of the surround speakers or the left and right front speakers can easily hear the high pitched whine every time someone speaks. Do you send FM stations through your surround sound system? Have you ever been reasonable in your life? channels' audio would be better quality than FM, but the BBC FM stations beat all the UK radio stations on all of the digital TV platforms and DAB. Hence the petition to get the BBC to increase their bit rates: What is needed is for DAB to be scrapped and replaced with a better system I agree with that. and this can best be achieved by a complete boycott of DAB revivers and stations. Unfortunately, that won't happen. After starting that protest off then we should demand that all BBC radio stations are broadcast in AAC+ using Dolby 5.1 encoding so that they can allow the listener to experiences DVD-Audio and SACD recordings. It's not going to happen, because they've backed DAB and they will make sure it sells. Radio via broadband is the best system for delivering high quality, including surround sound in future no doubt. Delivering multimedia via the Internet has the advantage that users have a wide variety of codecs they can use, and media players adopt new codecs as and when they're released. Add the fact that broadband connection speeds are rapidly increasing, and that the BBC is planning to use multicasting to distribute live streams for BBC1 and/or BBC2 then in the next few years it almost inevitable that we will have the highest quality radio via broadband. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Please sign the petition asking the BBC to provide better audio quality on its radio stations on DAB, Freeview, satellite and cable: http://tinyurl.com/a68e4 |
Audio compression does not even give FM quality
Community radio stations usual broadcast direct so they would offer the best sound quality of all. That doesn't necessarily hold true. Smaller community stations tend to have lower budgets and may well use lower bit rates for their distribution (for example, 256kb/s). They may even use MPEG codecs for these links. It's also possible that the source material won't be as high a quality, with material sourced from MP2 based playout systems or Minidisc (or, heaven forbid, MP3s). Larger groups, on the other hand, will have a greater budget to spend on distribution. Remember that buying bandwidth in bulk can reduce the relative costs per station, and these groups also need to buy bandwidth for their IT infrastructures. They are also more likely to use linear audio for playout (or at least an APTX based system, which is far better than MPEG). |
Audio compression does not even give FM quality
"DB" wrote in message ... Community radio stations usual broadcast direct so they would offer the best sound quality of all. That doesn't necessarily hold true. Smaller community stations tend to have lower budgets and may well use lower bit rates for their distribution (for example, 256kb/s). They may even use MPEG codecs for these links. It's also They tend to use FM links or direct connections to the transmitters. possible that the source material won't be as high a quality, with material sourced from MP2 based playout systems or Minidisc (or, heaven forbid, MP3s). Only for commercials. All the community radio DJ's I know play directly from CD. Its the BBC that now plays most of its local radio content from mp3's. Larger groups, on the other hand, will have a greater budget to spend on distribution. Remember that buying bandwidth in bulk can reduce the relative costs per station, and these groups also need to buy bandwidth for their IT This has nothing to do with the way community radio works. Community radio is not commercial radio and groups cannot buy out other community radio stations. Ofcom will not allow it. infrastructures. They are also more likely to use linear audio for playout (or at least an APTX based system, which is far better than MPEG). |
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