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What is the difference between 128k and 320k music? Part 2

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What is the difference between 128k and 320k music? Part 2

Bit Rate

In simple terms, we can think of a sound wave as a curve.

Bit Rate

We know that the curve is made up of points, and the sampling rate is the number of points in the middle of the length per second (the horizontal axis in the figure above). Sampling precision is the number of points in the dynamic range (upper vertical axis). The finer the positioning of these two dimensions, the greater the true sound restoration and the better the sound quality. Of course, the larger the audio file will be. The customer mentioned by the above colleague said that the latest Hi-Res Audio format released by SONY is a 6-channel 192kHz/24-bit recorded audio file. The size of the lossless format, of course, will be more than 200 megabytes.

The sampling frequency is approximately the following depending on the type of use (k is the thousand-bit symbol, 1khz=1000hz):

8khz: used for phones etc, is enough to record human voices.

22.05khz: transmission use frequency.

44.1kb: Audio CD.

48khz: used in DVD and digital TV.

96khz-192khz: used for DVD-Audio, Blu-ray HD, etc.

The common range of sample precision is 8 bits to 32 bits, with 16 bits generally used on CD.

Having said that, my friends are starting to get confused. It’s not the bitrate that determines the sound quality, so why is everyone saying that 320kb sound quality is better than 128kb?

【Audio Compression】

Well, in fact, the bit rate should be said to be another dimension, it is a compression of audio files.

Nowadays, most of the audio formats we use regularly are based on the original “WAV” file of the audio CD (44.1khz sample rate, 16bit sample precision, 2ch). The original recorded sound data is stored in a matrix, which is in PCM format, while WAV format is an encoding format developed by Microsoft. Its function is to reproduce the data in PCM format through encoding.

Since the data in WAV basically completely restores the PCM data, MP3, AAC and other lossless encoding formats are basically recompressed based on the WAV files. Therefore, we can simply think that WAV is the original audio format and other audio formats are compressed formats.

When it comes to compression, storage and transmission are inseparable. The purpose of compression is to improve storage and transmission, so before we talk about compression, we need to understand the basic units of computers.

We all know that the computer is a binary number system, and the files stored by the computer are made up of two numbers, 0 and 1. Therefore, the computer’s transmission is based on each number, and each number is called 1 ” bit”. For example, for an audio piece, its basic data is “0,1,1,1,0,1, 1 ,0”, and when transmitting, these numbers are transmitted one by one. The sampling precision mentioned above is this unit.

The storage unit of the computer is “byte (Byte)”. In the computer, 1 byte consists of 8 bits, that is, 8b(bit)=1B(Byte). In computer parlance, data storage is expressed in decimal and data transmission is expressed in binary, so 1KB=1024B=1024×8b. This is also part of the reason why the hard drive capacity we see does not match the actual capacity.

Go back and talk about audio compression, the bitrate of the audio is actually the compression ratio. So the bitrate really just defines the size of the file, but because under normal conditions the larger the file, the less data you lose, so the sound quality is relatively higher. However, the bit rate itself does not directly affect the quality of the file. For example, if we take a 128kb file as the source file, even if it is converted to a 320kb file, the sound quality will not be better than 128kb. .

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What is the difference between 128k and 320k music?

Bit rate comparision

192k is a turning point. Below 192K, the sound quality is relatively damaged, especially the high-frequency part above 16Khz will be cut off.

bitrate

In a nutshell, mp3s above 192k can no longer be listened to with CD sound quality on ordinary home devices, except for Golden Ears and Hifi devices. Of course, these data are not 100% reliable. There are always people on the internet sharing fake mp3 above 192K. In fact, they are converting low bitrate music to high bitrate through software, but the sound quality will not improve. be improved. Windows Media Player compresses it. The resulting mp3 is absolutely wonderful, no matter how high the compressed bitrate is, it will cut perfectly around 16K.

Some time ago, a colleague came across a very troubled client. The mess was said to have been caused by the client asking him to provide song files larger than 100MB-200MB in size. And my colleagues don’t know much about audio formats, so they started endlessly fumbling about FLAC, WAV and audio size. In the end, the colleague did not explain to the client what was going on.

After that, other things happened that made me feel that in the music industry there are too many practitioners around me who have an extremely poor understanding of music and even lack some basic knowledge related to music. I don’t even have the idea to understand, which makes me very sad. It seems that music has only one merchandise attribute, and our practitioners only need to organize the shelves, encode various merchandise, and use the big data of users’ purchase records to recommend merchandise to users, no matter why to users. they like this. features that these products have, and use cold data to provide users with various services.

Therefore, I think it is necessary to write something. I don’t expect practitioners to become people who really love music. I just hope that even if you still think of “her” as a commodity, you can first figure out what you’re selling. and what is..

PS: The content of the first lesson is about media files. Since the relevant content involves a lot of technical stuff, it seems a bit boring, but if you read it carefully, you will find that it is actually very easy to understand, but this basic knowledge can be very helpful.

Bit Rate, Sample Rate, Lossless, MP3, FLAC, APE, 320kb, 192kb, 128kb, 44.1khz, CBR, VBR. Does this bunch of various names make you both familiar and unknown?

The higher the bitrate, the better the sound quality. Lossless music is the highest sound quality, right? So, let’s start with the sound collection.

【Audio composition】

Nowadays, when we talk about audio, everything is digital audio. Digital audio consists of three parts: sample rate, sample precision, and number of sound channels.

Sample Rate: Both the sample rate, which refers to the number of samples per second when recording the sound, expressed in Hertz (Hz).

Sampling Precision: Refers to the dynamic range of the recorded sound, measured in bits (Bit).

MP3 and knowledge of the effects of possible settings

The MP3 audio compression method (also called MPEG-1 Layer 3) uses the properties of the human ear to save storage space. Frequencies inaudible to humans are filtered out of musical pieces. Depending on the degree of compression (so-called bit rates), this leads to no or severe loss of quality.
Music CDs use a constant bit rate (consumption of storage space / unit of time) of 1.4 Mbit per second for a stereo audio signal.

In comparison, a data rate of 192 kBit / s is sufficient with MP3 for almost CD quality music. It follows that the memory requirement is also significantly lower. There is about 10MB per minute of music on a music CD, good quality MP3 files only occupy about one eighth of this memory; So you can put around 8 hours of music on an MP3 CD.

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A distinction is made between:

VBR – variable bit rate (variable bit rate)

With VBR, the bitrate constantly adapts to the music. Fewer bits are used in more “quiet” places (for example, few instruments or quiet passages), so the bit rate is lowered, while in more complex places the bit rate is increased as much as is necessary for the specified quality level is maintained at all times. Therefore, the MP3 file created in this way requires less storage space than MP3 files of comparable quality. The size of the final file is of course unpredictable and can vary greatly depending on the song and its genre. (is better than ABR and CBR)

ABR: average bit rate

ABR makes it possible to use variable bit rates but still meet the given average bit rate very precisely. In this way, the encoder saves bits in quiet places, which are then available to more complex places. The quality of this mode is between CBR and VBR, since the disadvantages of the CBR mode are eliminated, but the advantages of VBR mode only partially come into play, since the higher bit rates are used less frequently so as not to exceed the specified average bit rate. (is better than CBR)

CBR – constant bit rate

In “old-fashioned” CBR mode, a certain bit rate is used, regardless of what bit rate is actually required. As a result, higher bit rates are not available for complex locations, which is at the expense of quality, while bits are wasted in quiet locations, which is at the expense of file size.

Conclusion: the best method is VBR.

The only exception is the CBR bit rate (320 kbit / s), but this no longer makes sense.
other technical terms:

Joint Stereo

Joint stereo, also known as MS stereo, is a lossless encoding of the two audio channels. The great similarity of the channels is exploited by creating two new channels. The sum of the left and right channels is stored in the middle channel (M); the difference between the original channels is encoded in the side channel (S). Therefore, the middle channel contains most of the information, while in the side channel there is only a small amount of information available. Both channels are quantized separately and relatively good compression is achieved.

However, this trick does not work for songs with strong channel separation, that is, if the left and right are almost not similar. Logically mid / side stereo is also not possible with mono.

Definition and explanation of the term bit rate

Bit rate denotes a unit in which the relationship between the amount of data and time occurs. It is measured in the unit of bits per second. Common abbreviations for bit rate are bit / s or bps. The output quantity of information units in relation to digital multimedia formats limited by a constant output time is designated on a timeline.

Bit rate is used in video and audio compression. Encoding is possible with constant (short CBR) and variable (short VBR) bit rate. The variable bit rate aligns the encoding with the content of the multimedia content. In the case of a predominantly quiet scene in a movie, for example, fewer units of information are required relative to time. However, in scenes with a lot of movement, the bit rate increases. This is intended to allow optimal use of storage space with high image quality at the same time when compressing with a codec. Often times the required memory space is also less when encoding with a variable bit rate compared to a fixed rate.

Constant bit rate

Constant bit rate describes a compression method for video and audio content during storage and transmission. A constant data rate is used, regardless of the complexity of the respective signal. The same amount of data is always produced per unit of time.

Constant bit rate is often used in multimedia broadcasts. The reason for this is the limited streaming capabilities. By using constant bit rate, optimal quality is achieved with the same data throughput. In some cases, however, it may also happen that amounts of data are “given away”. This is the case when the content to be encoded requires a lower rate than specified. This is especially true for videos with quiet scenes or very quiet audio files. The constant bit rate is used, for example, for video CDs or Internet radio.

Variable bit rate

In addition to the constant bit rate, encoding with a variable bit rate is also possible. Here is audio and video content in constant quality at different bit rates depending on the content stored or transmitted.

This solution has established itself in the media storage field as it offers higher quality with less memory consumption at the same time. When encoding with a variable bit rate, individual sections of a medium receive different compressions depending on the complexity of the content. This enables the highest possible quality to be achieved with low memory consumption.

For a long time, encoding with the help of variable bit rates was considered insecure. In the meantime, however, the technology has matured, so good results can also be achieved by converting a medium with a variable bit rate. The downside of this method is that you cannot predict before conversion how big the file will be in the end. In most cases, only a minimum and maximum bit rate can be set. Individual encoders also offer the option of specifying how large the file should be before converting it.

Average bit rate

A third compression method is the definition of an average bit rate. A medium is converted at a variable bit rate. This enables a fixed file size to be achieved while maintaining high quality. For this variant of media compression, some codecs offer the option to compress in two passes. This allows the average bit rate to be reached very precisely.

In the first pass, the material is analyzed and then compressed in the second. Basically the method corresponds to that of variable bit rate, but an average bit rate allows you to calculate the size of a file. A deviation tolerance can be specified for individual programs.

Nominal bit rate

Nominal bit rate indicates the average bit rate that is achieved by encoding with a variable bit rate. Despite the possible fluctuations that arise in the various VBR modes, a quality assessment can be made.

The nominal bitrate concept was introduced by the developers of the OggVorbis codec. This should make it easier for MP3 users to start using variable bit rate. Many Mp3 codec users were only used to compressing an audio file with a fixed bit rate.