PCM (Pulse-Code Modulation) and bitstream are both methods of transmitting audio data – so they’ve got something in common, at least.
Dive much deeper, however, and comparing PCM audio vs bitstream can get confusing.
In a nutshell, PCM can be considered more “fundamental” than bitstream formats like Dolby Digital or DTS. Dolby Digital and DTS are not bitstream-only formats. Each format can be carried over PCM from, say, a Blu-ray player over 5.1 or 7.1 RCA line-level outputs.
Separating the audio quality differences between PCM and bitstream is not clear-cut, as they serve somewhat different purposes.
This is because PCM is a raw, uncompressed form of digital audio that directly represents the analog audio waveform. It’s a basic building block for digital audio and is widely used in various applications, from high-quality audio recording to telecommunication.
On the other hand, bitstream formats often involve additional processing, encoding, and potentially compression to serve specific needs, such as reducing file size or supporting multi-channel surround sound.
As ever, there’s more to it than that – so let’s dive in!
Table of Contents
Deep Dive into PCM and Bitstream
Overview of PCM (Pulse-Code Modulation)
PCM is a digital representation of an analog signal where the magnitude of the signal is sampled at regular intervals and then quantized to a series of symbols in digital (usually binary) code.
- Definition: PCM is a method used to digitally represent analog signals. In the context of audio, this means it’s a digital representation of the audio waveform.
- Where It’s Used: PCM is commonly used in CDs, Blu-ray discs, WAV files, and other high-quality audio sources.
- Processing: Audio data in PCM form is often raw and uncompressed, but it can be compressed, too.
- Quality: PCM can offer high-quality sound output, assuming a high enough bitrate and sample rate.
- Compatibility: Most devices that can play digital audio can handle PCM data.
Technical Parameters of PCM
- Bit Depth and Sample Rate: In a PCM setup, you can sometimes adjust settings called “bit depth” and “sample rate.” Think of these like the resolution settings for your audio; higher numbers usually mean better quality. Bit depth and sample rates are determined by the restrictions of the media format itself, for example, CD, DVD, or Blu-ray. PCM can support up to 24-bit/192kHz of uncompressed audio.
- Channels: PCM can support multi-channel audio – often up to 8 channels for 7.1 surround sound systems. This configuration includes seven full-range channels and one LFE subwoofer channel.
- Discrete Sampling: In PCM, each audio channel is individually sampled, encoded, and stored as separate data. This means that the sound you hear from each speaker is precisely what was intended to be sent to that specific channel. There is no mixing or “matrixing” of channels. For example, in a 7.1 PCM setup, each of the seven full-range channels and the one low-frequency effects (subwoofer) channel are kept entirely separate.
Overview of Bitstream
- Definition: Bitstream is a stream of data bits in compressed audio formats like Dolby Digital, DTS, Auro-3D, Dolby Atmos, and DTS:X.
- Where It’s Used: Bitstream is used in DVDs, games, Blu-rays, and streaming services that offer multi-channel audio.
- Processing: Bitstream is encoded in a specific audio format. When you select bitstream output, you ask the source device to pass the audio data in its original compressed form to be decoded by an external device like an AV receiver.
- Quality: The quality of a bitstream depends on the encoding and may lose some quality due to compression.
- Compatibility: Not all devices can decode all types of bitstream audio. You will need an AV receiver compatible with the specific audio format.
Technical Parameters of Bitstream
- Encoding Formats: Unlike PCM, bitstream can carry encoded audio formats like Dolby Digital, DTS, Auro-3D, and Dolby Atmos. Encoding includes additional metadata that can be used for things like dynamic range compression or even object-based audio, providing a more adaptable experience for newer surround-sound setups.
- Channels and Matrixing: Bitstream can support various channel configurations based on the encoding method chosen and may use matrix encoding to combine multiple audio channels into fewer channels.
- Spatial Audio: The metadata in encoded bitstream audio can include information for rendering spatial or object-based audio, such as Dolby Atmos. This makes bitstream potentially superior for creating a more immersive, 3D audio environment – but that depends on your setup.
- Decoding Requirement: One caveat with bitstream is that your AV receiver must be capable of decoding the specific bitstream format you use. Otherwise, you won’t be able to take advantage of the features the encoded format offers.
Comparison of PCM and Bitstream
Bitstream and PCM operate differently regarding where the audio decoding occurs, how they deal with channel information, and the range of audio formats supported.
Let’s take a closer look:
The Role of Encoding and Compression
PCM’s lossless audio retains every detail of the original recording.
Conversely, bitstream can either be lossy (Dolby Digital, DTS) or lossless (Dolby TrueHD, DTS-HD Master Audio).
Lossy bitstream formats are more common in older or bandwidth-limited applications, like DVDs or digital TV broadcasts.
Lossless bitstream formats are generally reserved for high-definition media, like Blu-ray discs, where storage space and data transfer rates are less of an issue.
As noted, one of bitstream’s unique advantages is its use of metadata – and this is critical to understanding when bitstream is sometimes preferred to PCM. Unlike PCM, which sends audio for each channel as-is, bitstream can include instructions that tell your AV receiver how to distribute the audio. PCM can carry only limited metadata.
For instance, a movie encoded in Dolby Atmos will include metadata to help the receiver send specific sounds to overhead speakers, creating a more immersive experience.
Where the Audio Decoding Occurs and Its Impact
PCM: Decoding in Source Device
In PCM sound configurations, the digital-to-analog conversion and digital audio decoding occur in the source device. This could be your Blu-ray player, gaming console, or smart TV.
This decoded audio is then sent uncompressed to your AV receiver, which primarily amplifies the signal before sending it to the speakers.
- Advantage: If the source device has a high-quality audio decoder, then using PCM could result in superior audio fidelity since you leverage the device’s superior decoding capabilities.
- Disadvantage: If the source device’s decoding capabilities are inferior to your AV receiver, you might not get the best possible sound quality.
Bitstream: Decoding in AV Receiver
In bitstream sound configurations, the source device does not decode the audio.
Instead, it sends the compressed and encoded digital audio stream to your AV receiver. The receiver then decodes into an uncompressed audio signal, which it amplifies and sends to the speakers.
- Advantage: Bitstream can be advantageous if your AV receiver has a more versatile audio decoder compared to your source device. This is often the case with high-end receivers supporting advanced audio codecs like Dolby TrueHD or DTS-HD Master Audio.
- Disadvantage: If your AV receiver has less decoding capabilities, then you won’t be able to take advantage of all the latest multi-channel codecs. The bitstream setup also shifts the burden of decoding to the receiver, which could introduce latency.
Handling of Audio Channels
PCM
PCM audio typically supports multi-channel formats, often up to 8 channels for 7.1 surround sound systems.
In PCM, each channel is sampled and stored separately, meaning no audio information is shared between the channels.
This leads to higher accuracy in audio reproduction, but it may not take advantage of advanced spatial audio formats like Dolby Atmos and DTS:X.
Bitstream
On the other hand, bitstream can leverage more complex audio formats, offering a potentially richer spatial audio experience if your setup supports it.
The Link Between Bitstream and Dolby or DTS Technologies
Bitstream is particularly relevant to those aiming to create a high-quality surround-sound setup, often using Dolby or DTS formats.
Dolby formats are types of bitstream audio that have been compressed and encoded using Dolby’s algorithms.
When you select bitstream as your audio output, you’re choosing for the audio to be passed through to your AV receiver or soundbar in a compressed, encoded form that contains metadata about how to distribute the audio.
Configuration Tips for Dolby/DTS Surround Sound
- Ensure your AV receiver or soundbar supports the Dolby or DTS format you’re interested in (e.g., Dolby Atmos, Dolby TrueHD).
- Use a high-quality HDMI cable capable of handling the Dolby formats.
- Go to the audio settings of your source device (TV, Blu-ray player, gaming console) and select bitstream as the audio output.
- Also, select the specific Dolby or DTS format you want to use if the option is available.
- On your AV receiver or soundbar, set it to auto-detect or specifically select the Dolby format for decoding.
Advantages and Disadvantages of PCM and Bitstream
So, what are the advantages and disadvantages of PCM and bitstream?
Advantages of PCM
- High Audio Fidelity: Being a lossless and uncompressed audio format, PCM ensures high audio fidelity, allowing you to experience sound closest to the original recording.
- Low Latency: Because it lacks the need for complex compression and decompression algorithms, PCM generally offers lower latency.
- Widespread Compatibility: PCM is the standard digital audio format for CDs and most computers, making it universally compatible with almost all devices capable of digital audio playback. Moreover, because PCM doesn’t need sophisticated decoding at the input, it’s a better solution for computer (PC) audio as well.
- Simple Signal Path: PCM maintains a relatively simple signal path by sidestepping additional encoding and decoding steps, reducing the likelihood of audio artifacts or other forms of signal degradation.
Disadvantages of PCM
- Large File Sizes: Due to its lossless and uncompressed nature, PCM files can be quite large, making them less practical for storage and transmission over limited bandwidth.
- Limited Support for Surround Sound: While multi-channel PCM does exist, not all systems and receivers support it, making it less versatile for complex home theater setups.
Advantages of Bitstream
- Efficient Storage and Transmission: Due to its compressed nature, bitstream audio files are smaller and easier to store and transmit, making them ideal for streaming and other bandwidth-sensitive applications.
- Surround Sound Support: Bitstream formats like Dolby Digital, DTS, and Dolby Atmos offer robust support for advanced multi-channel audio.
- Dynamic Range Compression: Some bitstream formats come with dynamic range compression features, which can make quiet sounds more audible, offering a more balanced audio experience in various listening environments. Many people find that bass levels are too invasive with PCM.
- Pre-Processed Effects: Some bitstream formats offer pre-processed audio effects like virtual surround sound, which can enhance the audio experience without needing high-end hardware. The discussion of bitstream vs PCM surround sound comes into its own for those with high-end AV receivers and 7.1+ speaker systems.
Disadvantages of Bitstream
- Loss of Audio Fidelity: The compression algorithms in bitstream formats can lead to a loss of audio details, resulting in a less accurate sound quality than the original recording.
- Latency: The need to encode and decode the compressed audio can introduce latency, which may be noticeable in real-time applications like gaming or live music performances.
Recommendations on When to Opt for PCM vs. Bitstream
As we’ve seen, the decision of whether to choose PCM or bitstream varies widely with different setups and use cases.
A simple solution? Try both – fiddle about with your audio settings and use your ears to learn which configuration sounds best for your setup, room size, etc.
Sometimes, the best-sounding setup isn’t what you expect it to be!
Here are some common examples of when to consider bitstream over PCM and vice versa:
Immersive Movie Watching
Preferred Format: Bitstream
Movies often come encoded with complex multi-channel audio formats like Dolby Atmos or DTS:X. Bitstream allows the AV receiver to decode and ‘use’ these formats.
This will enable you to extract the best from a home cinema setup with a speaker configuration that can take advantage of these formats, such as a 5.1.2 setup for Dolby Atmos.
Examples & Scenarios:
- Blu-ray Playback: You might be building a Dolby Atmos setup – some 4K UHD Blu-ray and standard Blu-ray video discs offer Dolby Atmos or DTS:X immersive audio soundtracks that require bitstream.
- Streaming Services: Some streaming services like Netflix and Disney+ offer Dolby Atmos or other advanced audio formats for certain titles.
Two-Channel Music Listening
Preferred Format: PCM
For music, especially high-definition tracks in formats like FLAC or ALAC, PCM offers the advantage of uncompressed audio. This will preserve the nuances and dynamic range of the music.
Examples & Scenarios:
- High-Resolution Audio Files: Listening to FLAC, ALAC, or other lossless formats via a digital music player or computer.
- CD Playback: CDs generally use PCM encoding, and PCM for playback ensures you’re hearing the audio as it was encoded on the disc.
Gaming
Preferred Format: PCM or Bitstream
In fast-paced or competitive gaming scenarios where every millisecond counts, PCM is often the better choice because it typically offers lower latency. Many gamers complain about the latency introduced by Dolby formats.
With that said, when latency isn’t an issue, and you want to take advantage of your complex sound system, bitstream will enable you to do that.
Example 1: High-Fidelity Music Playback for Two-Channel Audio
Preferred Format: PCM
Configuration:
- Speaker Setup: Stereo (2.0).
- Cable: HDMI, optical, or high-quality USB.
- Source Device Settings: Select PCM as the output.
- AV Receiver Settings: Choose a mode like “Stereo” or “Direct” to avoid additional sound processing.
Explanation: In a two-channel setup designed for music, PCM’s uncompressed audio output can deliver natural, lifelike sound. Bitstream encoding is of no benefit here.
Example 2: Gaming with 5.1 Surround Sound
- Speaker Setup: 5.1 (Five speakers and a subwoofer).
- Cable: HDMI.
- Source Device Settings: Can be set to either “Linear PCM” for less latency or bitstream for complex audio.
- AV Receiver Settings: Choose a gaming audio mode if available; otherwise, set it to auto.
Example 3: Watching TV Shows and Films on a 2.0 to 7.1+ Setup
Preferred Format: It varies
Configuration:
- Speaker Setup: 2.0 to 7.1 or higher.
- Cable: Typically HDMI ARC/eARC.
- Source Device Settings: Select bitstream for programs with surround sound soundtracks. If the content you are watching doesn’t support advanced audio formats like Dolby Atmos or DTS:X, then PCM would be a suitable choice, especially for setups that are not capable of handling these advanced formats.
- AV Receiver Settings: For bitstream, set the receiver to auto-decode the incoming format. For PCM, set your AV receiver to “PCM” or “Stereo/Direct” mode to ensure it decodes and processes the PCM audio signal directly.
Explanation: For standard stereo (2.0) or basic surround sound (up to 7.1), PCM can handle the audio well since it can carry up to 8 discrete channels of audio. This is sufficient for most surround sound formats.
However, for more complex audio formats like Dolby Atmos or DTS:X, which include additional elements like ceiling sounds and more detailed spatial audio, PCM isn’t sufficient.<?p>
Testing The Differences Between PCM Audio vs Bitstream
Here’s some guidance on how to gauge the differences between PCM audio vs bitstream for when your immediate instincts fail you – which happens to even the best-trained audiophiles and engineers!
Listening Tests
- Equipment Setup: Use high-quality speakers or headphones connected to an AV receiver that supports both PCM and bitstream formats.
- Source Material: Choose audio tracks with various sound elements, from low bass to high treble and subtle to intense dynamics.
- Volume Leveling: Utilize a decibel meter to ensure the volume is consistent when you switch between PCM and bitstream.
- Blind Testing: Consider enlisting a helper to switch between audio formats to ensure the test remains impartial.
- Repeat Tests: Get your friends and family involved to conduct the test multiple times with different people to eliminate bias.
Conclusion
And there we have it: the comprehensive guide to PCM audio vs bitstream.
Ultimately, choosing between PCM and bitstream depends on your specific needs and your equipment. Neither is objectively better or worse than the other.
To discuss specific use cases for either PCM or bitstream, including any issues or peculiarities you’re experiencing, hop onto HomeTheaterForum.com and get involved in the community!
Key Takeaways:
- PCM: Good for high-fidelity music and simple setups. It’s also beneficial for low-latency requirements like competitive gaming. The source device performs the decoding.
- Bitstream: Better for advanced surround sound systems and for leveraging high-end AV receivers. The receiver performs the decoding.
Suggestions:
- Assess your equipment: Know the decoding capabilities of both your source device and your AV receiver.
- Match with Content: Use PCM for high-fidelity music and bitstream for immersive movies or games with advanced audio formats.
Experiment: If in doubt, try both settings with different media types to find what sounds best to you.
FAQ
1. Can I switch between PCM and bitstream easily?
Yes, you can usually switch between PCM and bitstream in the settings menu of your source device, like your TV, gaming console, or Blu-ray player.
2. Will choosing bitstream or PCM affect my video quality?
No, these settings are for audio output and have no impact on video quality.
3. Do I need a special receiver for PCM or bitstream?
Your receiver should generally support both, but check the specs. For bitstream, your receiver should support the specific audio formats you want to use (like Dolby Atmos).
Additionally, if purchasing a legacy receiver, it may only support 5.1 or 7.1 codecs via bitstream, not immersive.
4. PCM audio vs bitstream: Is one always better than the other?
Not necessarily. PCM can offer better quality for simple setups or high-fidelity music, while bitstream is better for advanced surround sound formats.
5. Bitstream vs PCM surround sound: Will PCM work for surround sound setups?
Yes, PCM supports surround sound, but it’s generally used for simpler setups and lacks extra features such as dynamic range compression. For advanced surround sound formats, bitstream is usually recommended.
6. What should I use for gaming: PCM or bitstream?
It depends on the type of gaming experience you’re after. PCM is sometimes better for fast-paced, competitive games where low latency is important. For immersive, cinematic gaming experiences, bitstream can be the better option, especially if you have an advanced surround sound setup.
7. Is bitstream better for Dolby Atmos setups?
Bitstream is the only choice for immersive audio like Dolby Atmos. This lets your AV receiver decode the Dolby Atmos audio tracks to take full advantage of your surround sound system.
8. Does PCM work with older equipment?
Generally, yes. PCM is a more straightforward, uncompressed audio signal that is widely supported, even on older equipment. However, you may need to check the maximum bit depth and sample rate your older equipment supports.
9. Do streaming services work better with PCM or bitstream?
Streaming services often offer a variety of audio formats. If you’re watching a movie or show with advanced surround sound formats available, bitstream would likely offer a better experience. For general streaming or music, PCM should suffice. Moreover, bitstream can transport wirelessly, while PCM is a wired solution only.
10. How does the audio cable type affect PCM and bitstream?
Optical cables might not support all advanced surround sound formats in a bitstream setup, whereas HDMI cables usually will. PCM is generally less affected by the cable type.
11. Will using bitstream introduce noticeable lag?
For most movie-watching experiences, the latency introduced by bitstream is negligible. However, PCM is usually recommended for lower latency in scenarios like competitive gaming, where every millisecond counts.
12. Is bitstream always compressed?
Not necessarily. The AV receiver does the decoding and could receive a lossless audio format like Dolby TrueHD, which is compressed but without loss of audio quality.
13. Can I use PCM for 5.1 or 7.1 setups?
Yes, you can. PCM can handle multi-channel audio, but you might miss out on some of the more advanced features of certain surround sound formats that bitstream can offer.
Sam Jeans is a freelance writer who has worked with prestigious clients such as the Royal Mint, The Independent, DailyAI, and top tech companies like Lenovo and Toshiba. With an MSc in International Development and Social Anthropology and a BA in Audio and Music Production, Sam brings a unique perspective to his writing, blending cultural knowledge with insights into audio engineering and the latest tech gadgets and trends.
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