These harmonics are above the Hi Michael, You seem to have a good understanding of sampling theory and the mathematics behind Fourier. These sort of debates however will rage on forever I suspect. The human ear cannot distinguish between a 22kHz sine, square or triangle wave. The second harmonic would be 44 kHz — inaudible, whether live, analog, or digital. A square wave has odd harmonics, so the lowest harmonic above the fundamental would be 66 kHz.
The lowest frequency that even needs to preserve a second harmonic would be around 10 kHz. The FIR interpolation filters will remove the higher harmonics, and reconstruct the waveform so you will get a pure sine wave on playback in any event. I have written an Ogg Vorbis encoder two years ago for a specific application. In Vorbis the MS stereo implementation is particularly clever, as you do the conversion only after you have already quantized your frequency values.
In effect this means that the conversion is lossless by its very definition. That was of course what would be expected. However, there was a big difference depending on the type of source material. All in all, typically two thirds of the resulting file contained M information, and one third S information. The only reason I know this is that I researched the matter when creating my own encoder. MP3 files are slightly different because MS stereo is handled at a different stage of compression.
Due to this the results are not bit-accurate, but for the same file size, and using a proper encoder, MS stereo still will give better results. Thanks for taking the time to add such a comprehensive reply. Using full stereo will give much improved spatial separation and enable you to pin point instruments at different spatial positions in the mix with greater accuracy, but to achieve full stereo you will be using almost double the bit rate.
Some encoders handle joint stereo in a bad way it is lossy after all. Joint Stereo itself is technically lossless. Consider this. You have a sample of digital audio where the left channel has a value of 16 and the right 8. Joint stereo encodes as the sum and difference of the two channels. In this case, the sum is 24 and the difference is 8. However, the computer must allocate enough space to store both values exactly or all that losslessness would be in vain.
Assuming we are dealing with 16 bits per channel per sample integer audio the most common type , to do this in all cases including the worst case we would need 17 bits for the sum channel and 16 bits for the difference channel.
This means we would actually need MORE space to store joint stereo than plain stereo. However, this is where the magic of data compression kicks in. This is where technologies like MP3 come in, though MP3 is a rather outdated technology Vorbis is better, spec-wise at least. These are lossy compression algorithms, and they can also usually compress joint stereo better by cutting out the less important data, especially in the difference channel , especially at lower bitrates.
The problem here is that the lossiness can be more noticable when using joint stereo, especially at very low and high bitrates as the article and other comments describe. I find that Joint Stereo works very well will even the highest bit rate. I swear by it. I think bitrate in combination with Joint Stereo is perfect. U can go full stereo with bitrate but i feel and hear no audible difference between them.
My ears are good at tuning in the quality of music. You can go full stereo at bitrate but trust me joint stereo isnt a bad choice either. One day we will go completely to 5. That would be the holy grail of sound. I have noticed the technology is hear with the advance of 5. It might be even nice that one day they will have decoders that decoded regular mp3 straight to 5. That would even be a much better technology. To get to my point Joint stereo is very good and dont be scared to use with with bitrate.
This technology is very good right now while its still available free. Thanks very much for the explanation, Richard. FYI, your blog entry came up second under a Yahoo!
Thanks Melinda. That was a very clear explanation to the concept of joint stereo. This is way more technical than I needed it to be. I was looking for a simple explanation of the differences in the formats, not a complete education in psycho-accoustics as applied to recording technologies in a class 1 cleanroom. Well, I hope it managed to increase your understanding of joint stereo a little bit more. Quality is important to me the higher the bitrate the better mostly kbps in normal stereo.
Then I convert my favorite ones to kbps Stereo using Audacity with a Lame encoder then transport it to my Walkman mp3 player! Happy happy joy joy. Fact now is more for compressed lossless because of larger storage space and increased network bandwidth over older 56k modems that mp3 was designed for.
If it is stereo keep it stereo, forget the joint stereo where it reduces the stereo image further, I have noticed this and the reason for looking for the answer. Thank you for providing this answer joint is make some parts of stereo recording mono to save space.
Though better to use ape or FLAC to keep the recording lossless keeping the original file untouched. Because the audio is so similar, when you export your audio as a joint stereo file, the media encoder is able to find the average of the Left and Right channel data and merge this into a smaller file.
Generally, joint stereo is more advantageous to use at a lower MP3 bitrate because the amount of data being averaged is already significantly lower. These advantages will depend on your content though. Unfortunately, it depends. The compression engines in your audio encoding software can drastically change the sound quality of your file audio files. Some of the compression engines do a better job at encoding audio in joint stereo while others do not.
If you have a good media encoder, you may not notice much of a difference between the joint stereo and stereo files. Finally, Intensity stereo coding is a method that achieves a saving in bitrate by replacing the left and the right signal by a single representing signal plus directional information. This replacement is psychoacoustically justified in the higher frequency range since the human auditory system is insensitive to the signal phase at frequencies above approximately 2 kHz.
Intensity stereo is by definition a lossy coding method thus it is primarily useful at low bitrates. For coding at higher bitrates only mid-side stereo should be used. Personally, after any audio registration, if I want to keep those audio files also in MP3 audio format, I use always Kbps of bitrate, CBR, 44Khz of sample rate, 24 bit depth and Joint Stereo coding.
In general, there is no more reason to still use normal Stereo coding, because the efficiency provided from Joint Stereo coding, in terms of storage, and overall better quality available bits per second are better managed during the encoding process are the two major advantages of this coding type and that explains also why a lot of audio processing software, while encoding a RAM audio stream into a compressed one like the MP3 format, will give you Joint Stereo as default choice, also with the hightest bitrate available.
Even if this is officially possible, using for example open source professional software like Audacity, doing this starting from a compressed audio stream, such as MP3s, we need to consider to start, for any kind of encoding or audio manipulations, from raw audio stream , for example from an uncompressed audio version, like WAV audio format.
If we consider Audacity, if we still have the original Audacity Project ,. NOTE: if, after the actual recording phase, we want to export, in Audacity , the audio stream in RAW format the hightest quality possible of your recordings in digital audio, with no headers or metadata available , we can do that by simply selecting " Other uncompressed file types " in the Export Audio dialogue, then checking the type under the Format Options section.
A first way to get some useful properties about MPEG files audio , and even if audio file is Joint Stereo or not, is to use an old, but useful, software called EncSpot a mirror download will be available at the end of this article. It is a quite old piece of software , but this does not mean that it does not work anymore! It has a graphical interface built around an improved version of mp3guessenc improved at the time - the current version of mp3guessenc, which is still being developed, is much more advanced than Encspot ever was.
The main feature is trying to guess which encoder was used to encode an MP3 file. To do that, it analyzes tags, flags and usage of MP3 features that tend to be typical of one encoder or another. In the following example it is shown the output of the sample command " EncSpotConsole.
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