WO2021220013A1

WO2021220013A1 - Digital audio converter assembly particularly for portable device

Info

Publication number: WO2021220013A1
Application number: PCT/GB2021/051050
Authority: WO
Inventors: Eric Curmen JOHNSON; Bryn James GRIFFITHS
Original assignee: Helm Audio Ltd
Current assignee: Helm Audio Ltd
Priority date: 2020-04-30
Filing date: 2021-04-30
Publication date: 2021-11-04
Anticipated expiration: 2022-10-30
Also published as: GB202006398D0

Abstract

A digital audio signal converter assembly is described. The assembly comprises a digital signal input, an analog signal output jack and a digital audio converter module. The digital audio converter module and the analog signal output jack are mounted on a circuit board and have a connection therebetween provided by the circuit board. The digital audio converter module is further connected to the digital signal input by a data signal carrying cable. The digital audio converter module is configured to convert digital audio received via the digital signal input to one or more analog signals prior to outputting the one or more analog signals via the analog signal output jack.

Description

Digital Audio Converter Assembly Particularly for Portable Device

Technical Field

The present invention relates to a digital audio converter and in particular to an external digital-audio converter for use as an adjunct with portable devices such as mobile telephones, portable music devices, tablet and laptop computers, and the like.

Background to the Invention

The advent of ever more sophisticated portable electronic devices, such as smartphones and tablet computing devices, has resulted in these devices being used for a multitude of applications, including the listening of music, films and so on.

In addition to devices themselves becoming more sophisticated, so too are the delivery formats improving in terms of both audio quality and bandwidth consumption. Audio files are typically recorded or encoded in digital form. This is not only for ease of storage but also for compatibility with the data communications networks over which they are delivered which are also digital.

In recent years, audio files have been encoded using the MP3 file format. MP3 was considered an improvement over earlier digital audio formats such as WAV files as it used compression that enables large audio files to be compressed into sizes that were deliverable over networks that (at least at the time) had limited bandwidth. However, the compression applied resulted in degradation of quality of the rendered audio.

New data formats are now being adopted that seek not only to minimise file size but also to minimise impact on the encoded audio so that the output device has opportunity to render the audio as close as possible to the original studio quality audio.

One such audio data format is the MQA (Master Quality Authenticated) format. Rather than being a competing file format, MQA format data can be packaged inside carrier formats such as WAV, FLAC, Apple (RTM) Lossless etc. However, compatible hardware and/or software at the output device is needed in order to convert the digital audio file into an analog signal that can be rendered by a speaker, headphones etc.

One particular problem with next-gen formats such as MQA is that although they are capable of delivering extremely high quality digital audio to users, the formats are evolving too fast for devices themselves to have hardware support for them and software converters lose much of the delivered resolution during the conversion process.

Although external digital-to-analog-converters (DACs) exist, they are typically bulky and often require a separate power supply.

Summary of the Invention

The present invention seeks to provide improved audio signals from an electronic device, such as but not limited to a mobile telephone, a portable music device, a tablet or laptop computer, and so on.

According to an aspect of the present invention, there is provided a digital audio signal converter assembly comprising a digital signal input, an analog signal output jack and a digital audio converter module, the digital audio converter module and the analog signal output jack being mounted on a circuit board and having a connection therebetween provide by the circuit board, the digital audio converter module being further connected to the digital signal input by a data signal carrying cable, the digital audio converter module being configured to convert digital audio received via the digital signal input to one or more analog signals prior to outputting the one or more analog signals via the analog siognal output jack.

Preferably, the digital audio converter module is sized such that it appears part of the analog audio jack housing.

In a preferred embodiment of the present invention, the digital analog converter module (DAC) is part of a connector cable. One end of the connector cable is terminated with a digital connector such as a USB-C connector for connection to a portable device such as a mobile phone. The other end of the connector cable is terminated with an analog audio connector such as a 3.5mm audio stereo adapter. The DAC is between the digital and audio connectors. A digital signal carrying cable connects the digital connector to the DAC.

It will be appreciated that other digital connector types could be used such as other USB/USB micro variants or the MFi connector.

A problem for users of portable devices is: how do they stream audio formats such as MQA without having a bulky non-efficient solution? Embodiments of the present invention seek to provide a plug and play solution that can operate with existing hardware and provide retro-fit compatibility for new audio formats. Preferably, power is obtained via the digital connector from the mobile device such that external power required. Preferably, the audio connector is configured to accept a 3.5mm male connector such that the cable can act as an adapter for mobile devices without headphone jacks and also provide improved sound quality in comparison to the mobile device’s existing audio output. It will be appreciated that the audio output need not be a 3.5mm jack and could take other forms.

In a preferred embodiment, the converter apparatus connects to a computing device such as a mobile phone via a digital data port. Audio data is configured to be sent to the converter assembly as a digital signal (using for example a USB type C, A or MFI connector). This passes along the digital signal carrying cable of the converter assembly and input directly to a circuit board which is encased inside a module in the converter assembly. On the other side of the module is a female 3.5mm into which the user may plug in a headphone jack.

The inventors have identified that by having the circuit board physically at or adjacent to the analog audio output, cross talk can be limited. The digital input to the circuit board is a relatively slow 44Khz digital signal which has less likelihood of causing cross talk. Preferably, board level L/R outputs analog signals are output directly to the 3.5mm female jack and on to the user’s headphones, speaker etc. In this design there is little opportunity to allow crosstalk and it has been found that the circuit in the form of a PCB can be configured to have an excellent separation of signal path, producing much better crosstalk results. Nominal crosstalk for this type of design is -70db to -80db. Preferably, the digital signal carrying cable is a shielded cable such as a silver-shielded cable. Preferred embodiments seek to provide a cross talk close to -100db. Further refinements are also possible. In one embodiment, the PCB includes multiple oscillators. In a multiple oscillator design, one oscillator is preferably configured to operate at substantially 44.1kFlz based and one at substantially 48kFlz. Use of multiple oscillators enables an improved clock reference to be captured for the DAC circuit.

As the assembly is preferably incorporated into a connector cable that is between the device and the audio output device, the cable is much easier to handle and can be used on the go. The preferred implementations are light enough to not have to use an extra hand to carry and can be operated by a single hand.

The preferred embodiments, therefore, provide an in-line DAC (ail in one cable) able to convert formats such as MQA and deliver high resolution audio with minimised crosstalk.

Other features, aspects and advantages of the teachings herein will become apparent to the skilled person from the specific description that follows.

Brief Description of the Drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a digital audio converter assembly according to an embodiment;

Figure 2 is a schematic diagram showing aspects of the embodiment of Figure 1 when in use; and,

Figure 3 is a PCB schematic illustrating selected aspects of a preferred embodiment.

Description of the Preferred Embodiments

Figure 1 is a schematic diagram of a digital audio converter assembly according to an embodiment.

The digital audio signal converter assembly 10 includes a digital signal input 20, an analog signal output 30 and a digital audio converter module 40 at the analog signal output 30. The digital audio converter module 40 is connected to the digital signal input 20 by a digital data signal carrying cable 50.

Figure 2 is a PCB schematic diagram illustrating selected aspects of a preferred embodiment.

Content providers often create music based on high speed studio recording. This recording is then converted to a format suitable for distribution and potentially streaming. An example is the MQAfile format. The file 100 is streamed to the mobile device or computer 110. In the case of the MQA format, the initial; step in decoding the format is referred to as “unfolding”. The mobile device 110 executes an app which is provided by the content provider (or some other service provider) to start the MQA unfolding process. Following the initial unfolding step, the data is communicated at an appropriate speed (typically 48Khz or 24Khz) via an output port 120 of the mobile device 110 to the digital signal input 20 of the assembly.

The digital signal is then passed along the digital data signal carrying cable 50 to the digital audio converter module 40 where it is converted via a digital-to- analog converter (DAC) to an analog output and on to an analog audio device such as headphones 130. Preferably, the digital audio converter module divides the signal so as to output stereo output signals to the analog audio device 130. In the case of MQA format data, the digital audio converter module 40 preferably does a second unfold operation on the signal prior to conversion. The unfolded signal can be recovered to studio recording level up to 386Khz.

The digital audio converter module is mounted on a circuit board with the analog signal output. Preferably, the digital audio converter module is physically adjacent the analog signal output to minimise cross-talk. Most preferably, the digital audio converter module is fed a fairly slow digital signal via the digital data signal carrying cable from the computing device. The digital data signal carrying cable is terminated on the circuit board (producing improved cross talk at the solder joint) and vias then connect to the digital analog converter. The signal is converted to a high speed analog signal by the digital analog converter which is in turn connected to an audio output, for example a 3.5mm audio jack which is also mounted on the circuit board. By soldering the 3.5mm connector directly to the board, this dramatically reduces the crosstalk since there are no open wires (vias on the circuit board connect to the pins of the female 3.5mm)

In a preferred embodiment of the present invention, the digital audio converter module 40 is part of a connector cable. One end of the connector cable is terminated with a digital connector such as a USB-C connector for connection to a portable device such as a mobile phone. The other end of the connector cable is terminated with an analog audio connector such as a 3.5mm audio stereo adapter. The module 40 is at the audio connector end of the cable with the circuit board inside what appears to be a housing for the audio connector jack. A digital signal carrying cable connects the digital connector to the module 40.

Further emi protection is preferably provided by shielding material such as a metal material about the housing which protects the circuit board from outside interference.

One implementation of a circuit board (in this case a PCB) for use in the embodiment of Figure 1 can be seen in Figure 3. I n the illustrated, preferred,

PCB schematic of Figure 3, U3 is the digital-analog converter, Y1 , Y2 and Y3 are OSCs. Preferably, these are, respectively, 48MFIz, 45.1584MFIz and 49.152MFIz. A female 3.5mm jack attaches to the board at J 1.

A problem for users of portable devices is how do they stream audio formats such as MQA without having a bulky non-efficient solution. Embodiments of the present invention seek to provide a plug and play solution that can operate with existing hardware and provide retro-fit compatibility for new audio formats. Preferably, power is obtained via the digital connector from the mobile device such that no external power required. Preferably, the audio connector is configured to accept a 3.5mm male connector such that the cable can act as an adapter for mobile devices without headphone jacks and also provide improved sound quality in comparison to the mobile device’s existing audio output. It will be appreciated that the audio output need not be a 3.5mm jack and could take other forms.

In a preferred embodiment, the converter assembly connects to a computing device such as a mobile phone via a digital data port. Audio data is configured to be sent to the converter assembly as a digital signal (using for example a USB type C, A or MFI connector). This passes along the digital data signal carrying cable of the converter assembly and input directly to a circuit board which is encased inside an audio connector housing of the converter assembly. Also on the circuit board and accessible via the housing is a female 3.5mm into which the user may plug in a headphone jack. The inventors have identified that by having the circuit board physically at the analog audio output, cross talk can be substantially limited. The digital input to the circuit board is a relatively slow (eg. 44Khz) digital signal which has less likelihood of causing cross talk. Conversion to analog and output to the analog output device happens on a compact, shielded, PCB so as to further minimise opportunity for noise and other interference.

Preferably, board level L/R outputs analog signals are output directly to the 3.5mm female jack and on to the user’s headphones, speaker etc. In this design there is little opportunity to allow crosstalk and it has been found that the circuit in the form of a PCB can be configured to have an excellent separation of signal path, producing much better crosstalk results. Nominal crosstalk for this type of design is -70db to -80db. Preferably, the digital signal carrying cable is a shielded cable such as a silver-shielded cable. Preferred embodiments seek to provide a cross talk close to -100db.

Further refinements are also possible. In one embodiment, the PCB includes multiple oscillators. In a multiple oscillator design, one oscillator is preferably configured to operate at substantially 45.1kFlz based and one at substantially 48kFlz. Use of multiple oscillators enables an improved clock reference to be captured for the DAC circuit.

As the assembly is preferably incorporated into an audio cable, the cable is much easier to handle and can be used on the go. The preferred implementations are light enough to not have to use an extra hand to carry and can be operated by a single hand. Optionally, the assembly may incorporate other functionality such as the applicant’s amplifier assembly which is the subject of GB 1906861.8 and is herein incorporated by reference. Should it be necessary, the assembly may optionally include a battery, this advantageously being a rechargeable battery. Embodiments may use a small lithium-ion 150mAh battery with an optimized battery charging circuit designed to reduce charging time with industry required circuit protection for shorting and thermal issues. Advantageously, where it includes a battery, the assembly may also include a charging port, which may be in the form of a USB-C connector or may be charged via the digital signal input when connected to the mobile device.

While the preferred embodiment locates the converter assembly in-line in the audio cable between the output of the sound source and the headphones, other embodiments could have a different arrangement. In one example, the headphones are Bluetooth™ enabled, in which case the assembly may be provided with a Bluetooth™ output unit. In this embodiment, the converter assembly can be in the form of a dongle attachable to the sound source.

Claims

1. A digital audio signal converter assembly comprising a digital signal input, an analog signal output jack and a digital audio converter module, the digital audio converter module and the analog signal output jack being mounted on a circuit board and having a connection therebetween provided by the circuit board, the digital audio converter module being further connected to the digital signal input by a data signal carrying cable, the digital audio converter module being configured to convert digital audio received via the digital signal input to one or more analog signals prior to outputting the one or more analog signals via the analog signal output jack.

2. The assembly of claim 1 , wherein the digital audio module is within the analog audio jack housing.

3. The assembly of claim 1 or 2, wherein the assembly comprises a connector cable for connecting an analog audio output device to a digital interface of a computing device.

4. The assembly of claim 4, wherein the digital signal input comprises a USB- C connector, a USB connector, a USB micro connector or a MFi connector.

5. The assembly of any preceding claim wherein the analog signal output jack comprises a 3.5mm audio stereo adapter.

6. The assembly of any preceding claim, wherein the digital audio converter is configured to convert MQA encoded digital audio to an analog signal.

7. The assembly of any preceding claim, wherein the circuit board includes board level L/R outputs from the digital analog converter to the analog signal output jack whereby analog signals are output directly.

8. The assembly of any preceding claim, wherein the data signal carrying cable is a shielded cable.

9. The assembly of claim 8, wherein the cable is a silver-shielded cable.

10. The assembly of any preceding claim, wherein the circuit board includes a plurality of oscillators configured to provide therebetween a clock reference to the digital audio converter.